Insurance Liabilities - Expected future benefits, expenses, and gross premiums (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
General Insurance
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	$ 3,099	$ 3,141
Undiscounted expected future gross premiums	4,275	4,112
Discounted expected future gross premiums (at current discount rate)	2,963	3,188
Individual Retirement
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	2,119	1,889
Undiscounted expected future gross premiums	0	0
Discounted expected future gross premiums (at current discount rate)	0	0
Group Retirement
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	315	324
Undiscounted expected future gross premiums	0	0
Discounted expected future gross premiums (at current discount rate)	0	0
Life Insurance
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	39,763	38,238
Undiscounted expected future gross premiums	29,789	28,584
Discounted expected future gross premiums (at current discount rate)	18,596	17,965
Institutional Markets
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	33,025	21,866
Undiscounted expected future gross premiums	0	0
Discounted expected future gross premiums (at current discount rate)	0	0
Other Operations
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits and expense	43,250	44,919
Undiscounted expected future gross premiums	2,141	2,305
Discounted expected future gross premiums (at current discount rate)	$ 1,372	$ 1,481