Income Taxes - Income Tax Expense by Fiscal Year (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Current:
U.S. federal	$ 1,504	$ 2,819	$ 2,377
State and local	243	219	291
Non-U.S.	843	754	629
Total current taxes	2,590	3,792	3,297
Deferred:
U.S. federal	184	(1,214)	1,607
State and local	28	(96)	66
Non-U.S.	2	23	25
Total deferred taxes	214	(1,287)	1,698
Total income tax provision	$ 2,804	$ 2,505	$ 4,995