Reserve for Future Policy Benefits and Contractholder Funds - Schedule of Account Values by Comparison of Current Crediting Rate to Guaranteed Minimum Crediting Rate (Details) $ in Millions	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 890	$ 878
Less than 3.00%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 0	$ 0
Less than 3.00% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0300	0.0300
3.00% - 3.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 34	$ 20
3.00% - 3.49% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0300	0.0300
3.00% - 3.49% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0349	0.0349
3.50% - 3.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 10	$ 11
3.50% - 3.99% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0350	0.0350
3.50% - 3.99% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0399	0.0399
4.00% - 4.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 437	$ 431
4.00% - 4.49% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0400	0.0400
4.00% - 4.49% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0449	0.0449
4.50% - 4.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 260	$ 266
4.50% - 4.99% | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0450	0.0450
4.50% - 4.99% | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0499	0.0499
5.00% or greater
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 67	$ 69
5.00% or greater | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0500	0.0500
Non-account balances
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 82	$ 81
At guaranteed minimum
Policyholder Account Balance [Line Items]
Account values with crediting rates	774	777
At guaranteed minimum | Less than 3.00%
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
At guaranteed minimum | 3.00% - 3.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
At guaranteed minimum | 3.50% - 3.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	10	11
At guaranteed minimum | 4.00% - 4.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	437	431
At guaranteed minimum | 4.50% - 4.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	260	266
At guaranteed minimum | 5.00% or greater
Policyholder Account Balance [Line Items]
Account values with crediting rates	67	69
At guaranteed minimum | Non-account balances
Policyholder Account Balance [Line Items]
Account values with crediting rates
1-50 basis points above
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 34	20
1-50 basis points above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0001
1-50 basis points above | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance above guaranteed minimum crediting rate	0.0050
1-50 basis points above | Less than 3.00%
Policyholder Account Balance [Line Items]
Account values with crediting rates	$ 0	0
1-50 basis points above | 3.00% - 3.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	34	20
1-50 basis points above | 3.50% - 3.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
1-50 basis points above | 4.00% - 4.49%
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
1-50 basis points above | 4.50% - 4.99%
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
1-50 basis points above | 5.00% or greater
Policyholder Account Balance [Line Items]
Account values with crediting rates	0	0
1-50 basis points above | Non-account balances
Policyholder Account Balance [Line Items]
Account values with crediting rates