Litigation, Claims and Contingencies - Summary of Components of Environmental Remediation Expense Included within Selling, General and Administrative Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Environmental Expense And Liabilities [Abstract]
Environmental expense		$ 2	$ 3
Accretion		0	0
Legal expense		2	1
Total expense		4	4
Insurance receivable	[1]	0	(1)
Total expense, net of receivable activity		$ 4	$ 3

[1] Activity of $0 denotes value less than $1 million.