CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Millions	12 Months Ended
Sep. 30, 2018 USD ($)
Non-cash investing activities:
Deferred purchase price of trade receivables sold	$ 436.7

Deferred purchase price of trade receivables sold where the receivables sold exceed collections.

No definition available.

Name:	wrk_DeferredPurchasePriceOfTradeReceivablesSold
Namespace Prefix:	wrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration