Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Leases [Abstract]
Leased capital assets included in net property, plant and equipment, primarily buildings and improvements	$ 17	$ 23
Total rental expense	$ 502	$ 402	$ 413