CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Millions	Dec. 31, 2018 USD ($)
Statement Of Cash Flows [Abstract]
Fair value of assets acquired, including goodwill	$ 5,910.2
Cash consideration for the purchase of businesses, net of cash acquired	(3,343.8)
Stock issued for the purchase of a business	(70.1)
Fair value of share-based awards issued in the purchase of a business	(70.8)
Deferred payments and unpaid working capital	16.6
Liabilities assumed	$ 2,442.1

Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

Name:	us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of liabilities assumed at the acquisition date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116869197&loc=d3e4845-128472

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_StatementOfCashFlowsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Business combination deferred payment and tax make whole payment and unpaid or unreceived working capital.

+ References

No definition available.

+ Details

Name:	wrk_BusinessCombinationDeferredPaymentAndTaxMakeWholePaymentAndUnpaidOrUnreceivedWorkingCapital
Namespace Prefix:	wrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business combination recognized identifiable assets acquired and liabilities assumed assets including goodwill.

+ References

No definition available.

+ Details

Name:	wrk_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsIncludingGoodwill
Namespace Prefix:	wrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business combination recognized identifiable assets acquired and liabilities assumed cash paid net of cash acquired.

+ References

No definition available.

+ Details

Name:	wrk_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCashPaidNetofCashAcquired
Namespace Prefix:	wrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of equity awards issued.

+ References

No definition available.

+ Details

Name:	wrk_FairValueOfEquityAwardsIssued
Namespace Prefix:	wrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant