Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Leases [Abstract]
Leased capital assets included in net property, plant and equipment, primarily buildings and improvements	$ 32	$ 17
Total rental expense	$ 467	$ 502	$ 402