Insurance Liabilities (Reconciliation of Policyholder Account Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 83,294	$ 75,209
Rollforwards Total
Policyholder Account Balance [Line Items]
Policyholder Account Balance	71,085	63,041
Funding agreements classified as investment contracts
Policyholder Account Balance [Line Items]
Policyholder Account Balance	11,245	11,151
Other investment contract liabilities
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 964	$ 1,017