Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 1,751	$ 1,456
Balance at end of period	1,853	1,602
Uncovered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	310	0
Covered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	175	352
Payments for legal matters	(383)	(206)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	1,621	1,441
Provision for legal matters	129	341
Payments for legal matters	(204)	(201)
Balance at end of period	1,546	1,581
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	110	11
Provision for legal matters	46	11
Payments for legal matters	(144)	(5)
Balance at end of period	$ 12	$ 17