<?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>0001628812</rptOwnerCik>
            <rptOwnerName>Murphy Ken</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WALGREENS BOOTS ALLIANCE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1 THANE ROAD WEST</rptOwnerStreet2>
            <rptOwnerCity>NOTTINGHAM</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>NG90 1BS</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP &amp; President, Global Brands</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
0001628812
Murphy Ken
C/O WALGREENS BOOTS ALLIANCE, INC.
1 THANE ROAD WEST
NOTTINGHAM
X0
NG90 1BS
UNITED KINGDOM
0
1
0
0
EVP & President, Global Brands
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