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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-11-04</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001020079</rptOwnerCik>
            <rptOwnerName>FOOTE WILLIAM C</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>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-11-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>88.36</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30823</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Transaction effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Kelsey Chin, attorney-in-fact</signatureName>
        <signatureDate>2015-11-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-11-04
0001618921
Walgreens Boots Alliance, Inc.
WBA
0001020079
FOOTE WILLIAM C
C/O WALGREENS BOOTS ALLIANCE, INC.
108 WILMOT ROAD
DEERFIELD
IL
60015
1
0
0
0
Common Stock
2015-11-04
4
S
0
3500
88.36
D
30823
D
Transaction effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.
/s/ Kelsey Chin, attorney-in-fact
2015-11-05