CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Millions	9 Months Ended
Jun. 30, 2018 USD ($)
Non-cash investing activities:
Deferred purchase price of trade receivables sold	$ 333.1

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