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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-11-01</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001628672</rptOwnerCik>
            <rptOwnerName>Pagni Marco Patrick Anthony</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>EVP, Global CLO and CAO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <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>41465</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2025-11-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>41465</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>41465</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The option vests with respect to 13,808 shares on November 1, 2016, 13,808 shares on November 1, 2017 and 13,849 shares on November 1, 2018, subject to the terms and conditions of the Walgreens Boots Alliance, Inc. 2013 Omnibus Incentive Plan, as amended (together with the related award agreement thereunder).</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
2015-11-01
0001618921
Walgreens Boots Alliance, Inc.
WBA
0001628672
Pagni Marco Patrick Anthony
C/O WALGREENS BOOTS ALLIANCE, INC.
108 WILMOT ROAD
DEERFIELD
IL
60015
0
1
0
0
EVP, Global CLO and CAO
Employee Stock Option (right to buy)
84.68
2015-11-01
4
A
0
41465
0
A
2025-11-01
Common Stock
41465
41465
D
The option vests with respect to 13,808 shares on November 1, 2016, 13,808 shares on November 1, 2017 and 13,849 shares on November 1, 2018, subject to the terms and conditions of the Walgreens Boots Alliance, Inc. 2013 Omnibus Incentive Plan, as amended (together with the related award agreement thereunder).
/s/ Kelsey Chin, attorney-in-fact
2015-11-03