Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 983	$ 914
Balance at end of period	1,027	909
Uncovered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	1	1
Covered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	146	10
Payments for legal matters	(103)	(16)
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	0	(7)
Balance at end of period	1,026	881
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	102	21
Provision for legal matters	1	10
Payments for legal matters	(102)	(9)
Balance at end of period	$ 1	$ 22