Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 1,751	$ 1,456
Balance at end of period	1,471	1,702
Uncovered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	10	0
Covered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	22	347
Payments for legal matters	(312)	(101)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	1,621	1,441
Provision for legal matters	0	341
Payments for legal matters	(160)	(101)
Balance at end of period	1,461	1,681
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	110	11
Provision for legal matters	22	6
Payments for legal matters	(126)	0
Balance at end of period	$ 6	$ 17