Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 983	$ 914
Balance at end of period	769	886
Uncovered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	1	3
Covered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	150	9
Payments for legal matters	(365)	(40)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	881	888
Provision for legal matters	145	0
Payments for legal matters	(262)	(7)
Balance at end of period	764	881
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	102	21
Provision for legal matters	5	9
Payments for legal matters	(102)	(28)
Balance at end of period	$ 5	$ 2