Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible amortization expense	$ 533	$ 552	$ 346
Estimated aggregate amortization expense in 2018	526
Estimated aggregate amortization expense in 2019	519
Estimated aggregate amortization expense in 2020	518
Estimated aggregate amortization expense in 2021	514
Estimated aggregate amortization expense in 2022	$ 503