Insurance Liabilities - Expected future benefits, expenses, and gross premiums (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
General Insurance
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	$ 3,350	$ 3,318
Expected future gross premiums	4,616	4,590
Individual Retirement
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	2,048	1,757
Expected future gross premiums	0	0
Group Retirement
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	317	317
Expected future gross premiums	0	0
Life Insurance
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	39,028	38,739
Expected future gross premiums	28,964	29,125
Institutional Markets
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	29,029	20,824
Expected future gross premiums	0	0
Other Operations
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefits and expense	44,148	45,468
Expected future gross premiums	$ 2,225	$ 2,389