Litigation, Claims and Contingencies - Summary of Components of Environmental Remediation Expense Included within Selling, General and Administrative Expense (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Environmental Expense And Liabilities [Abstract]
Net expense relates to divested businesses	$ 7	$ 5	$ 3