<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-10-30</periodOfReport>

    <issuer>
        <issuerCik>0001618921</issuerCik>
        <issuerName>Walgreens Boots Alliance, Inc.</issuerName>
        <issuerTradingSymbol>WBA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001124181</rptOwnerCik>
            <rptOwnerName>REED JAN STERN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WALGREENS BOOTS ALLIANCE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>108 WILMOT ROAD</rptOwnerStreet2>
            <rptOwnerCity>DEERFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, GC and Corp. Sec.</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2307</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10169</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4783</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                <sharesOwnedFollowingTransaction>
                    <value>14952</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2892</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17844</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>900</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>84.68</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16944</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F5"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18944</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-10-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>211</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>84.68</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18733</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>84.68</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-11-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>36858</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2018-11-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2025-11-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>36858</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36858</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on November 1, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Walgreens Boots Alliance, Inc. 2013 Omnibus Incentive Plan, as amended (together with the related award agreement, the &quot;Plan&quot;) had been satisfied. The shares underlying these restricted stock units will vest on November 1, 2017, subject to the terms and conditions of the Plan.</footnote>
        <footnote id="F2">On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on September 15, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Plan had been satisfied. The shares underlying these restricted stock units will vest on December 31, 2015, the first anniversary of the Second Step Closing Date (as defined in the Purchase and Option Agreement by and among Alliance Boots GmbH, AB Acquisitions Holdings Limited and Walgreen Co., dated as of June 18, 2012, as amended), subject to the terms and conditions of the Plan.</footnote>
        <footnote id="F3">Shares issued upon settlement of peformance share award (not a derivative security within the meaning of Rule 16a-1(c)) granted on March 1, 2013 under the Plan.</footnote>
        <footnote id="F4">Disposition relating to the satisfaction of tax withholding obligations upon the settlement of award granted in accordance with Rule 16b-3.</footnote>
        <footnote id="F5">On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on October 7, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Plan had been satisfied. In accordance with the Plan, 666 shares underlying these restricted stock units vested on October 30, 2015, 666 shares will vest on October 7, 2016 and 668 shares will vest on October 7, 2017, subject to the terms and conditions of the Plan.</footnote>
        <footnote id="F6">Includes shares acquired upon reinvestment of dividends and shares underlying restricted stock units issued in lieu of dividends (through September 30, 2015) on outstanding restricted stock units, including 158 shares with respect to the restricted stock unit awards described in notes (1), (2) and (5) above.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Kelsey Chin, Attorney-in-Fact</signatureName>
        <signatureDate>2015-11-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-10-30
0001618921
Walgreens Boots Alliance, Inc.
WBA
0001124181
REED JAN STERN
C/O WALGREENS BOOTS ALLIANCE, INC.
108 WILMOT ROAD
DEERFIELD
IL
60015
0
1
0
0
SVP, GC and Corp. Sec.
Common Stock
2015-10-30
4
A
0
2307
0
A
10169
D
Common Stock
2015-10-30
4
A
0
4783
0
A
14952
D
Common Stock
2015-10-30
4
A
0
2892
0
A
17844
D
Common Stock
2015-10-30
4
F
0
900
84.68
D
16944
D
Common Stock
2015-10-30
4
A
0
2000
0
A
18944
D
Common Stock
2015-10-30
4
F
0
211
84.68
D
18733
D
Employee Stock Option (right to buy)
84.68
2015-11-01
4
A
0
36858
0
A
2018-11-01
2025-11-01
Common Stock
36858
36858
D
On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on November 1, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Walgreens Boots Alliance, Inc. 2013 Omnibus Incentive Plan, as amended (together with the related award agreement, the "Plan") had been satisfied. The shares underlying these restricted stock units will vest on November 1, 2017, subject to the terms and conditions of the Plan.
On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on September 15, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Plan had been satisfied. The shares underlying these restricted stock units will vest on December 31, 2015, the first anniversary of the Second Step Closing Date (as defined in the Purchase and Option Agreement by and among Alliance Boots GmbH, AB Acquisitions Holdings Limited and Walgreen Co., dated as of June 18, 2012, as amended), subject to the terms and conditions of the Plan.
Shares issued upon settlement of peformance share award (not a derivative security within the meaning of Rule 16a-1(c)) granted on March 1, 2013 under the Plan.
Disposition relating to the satisfaction of tax withholding obligations upon the settlement of award granted in accordance with Rule 16b-3.
On October 30, 2015, the Compensation Committee determined that the performance criteria applicable to this restricted stock unit award granted on October 7, 2014 (not a derivative security within the meaning of Rule 16a-1(c) upon grant) under the Plan had been satisfied. In accordance with the Plan, 666 shares underlying these restricted stock units vested on October 30, 2015, 666 shares will vest on October 7, 2016 and 668 shares will vest on October 7, 2017, subject to the terms and conditions of the Plan.
Includes shares acquired upon reinvestment of dividends and shares underlying restricted stock units issued in lieu of dividends (through September 30, 2015) on outstanding restricted stock units, including 158 shares with respect to the restricted stock unit awards described in notes (1), (2) and (5) above.
/s/ Kelsey Chin, Attorney-in-Fact
2015-11-03