Debt and Financing Arrangements - Net Financing Charges (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Interest expense, net of capitalized interest costs	$ 36	$ 34
Banking fees and debt issuance cost amortization	3	2
Interest income	(2)	(1)
Net foreign exchange	(2)	(2)
Net financing charges	$ 35	$ 33