Debt and Financing Arrangements - Components of Net Financing Charges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Debt Disclosure [Abstract]
Interest expense, net of capitalized interest costs	$ 104	$ 118	$ 218	$ 228
Banking fees and bond cost amortization	14	11	27	41
Interest income	(5)	(5)	(14)	(12)
Net foreign exchange results for financing activities	2	(8)	0	(5)
Net financing charges	$ 115	$ 116	$ 231	$ 252