Restructuring and Other Costs - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring And Related Activities [Abstract]
Restructuring and other costs	$ 9.7	$ 17.9	$ 56.2	$ 107.1

Amount charged against earnings in the period for incurred and estimated costs, excluding asset retirement obligations, associated with exit from or disposal of business activities or restructurings pursuant to a program that is planned and controlled by management, and materially changes either the scope of a business undertaken by an entity, or the manner in which that business is conducted and other costs including but not limited to asset impairments, acquisition and integration costs.

No definition available.

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