Legal Matters - Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Loss Contingency Accrual [Roll Forward]
Balance as of beginning of period	$ 1,751	$ 1,456
Balance as of end of period	1,727	1,751
Uncovered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	322	21
Covered Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	248	1,024
Payments on legal matters	(594)	(750)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance as of beginning of period	1,621	1,441
Provision for legal matters	140	906
Payments on legal matters	(224)	(726)
Balance as of end of period	1,537	1,621
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance as of beginning of period	110	11
Provision for legal matters	108	118
Payments on legal matters	(146)	(19)
Balance as of end of period	$ 72	$ 110