Insurance Liabilities (Reconciliation of Policyholder Account Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 84,799	$ 83,294
Rollforwards Total
Policyholder Account Balance [Line Items]
Policyholder Account Balance	73,399	71,085
Funding agreements classified as investment contracts
Policyholder Account Balance [Line Items]
Policyholder Account Balance	10,116	11,245
Institutional group annuities
Policyholder Account Balance [Line Items]
Policyholder Account Balance	401	0
Other investment contract liabilities
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 883	$ 964