Fair Value Measurements - Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	$ 12,870	$ 12,132
Fair value of asset	24,271	22,845
Separate accounts	911	892
Top Hat savings plan mutual funds and common equity (included in Other assets)	62	57
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	7,150	6,869
States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	4,712	4,622
Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	574	183
Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	210	234
United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	204	191
Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	20	33
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	204	191
Fair value of asset	10,390	9,702
Top Hat savings plan mutual funds and common equity (included in Other assets)	62	57
Level 1 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 1 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 1 | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 1 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 1 | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	204	191
Level 1 | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	12,666	11,941
Fair value of asset	13,881	13,143
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Level 2 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	7,150	6,869
Level 2 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	4,712	4,622
Level 2 | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	574	183
Level 2 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	210	234
Level 2 | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 2 | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	20	33
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Fair value of asset	0	0
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Level 3 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 3 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 3 | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 3 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 3 | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Level 3 | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	10,124	9,454
Equity securities | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	378	387
Equity securities | Level 1 | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	10,124	9,454
Equity securities | Level 1 | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Level 2 | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Level 2 | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	378	387
Equity securities | Level 3 | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Level 3 | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Separate accounts taxable fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	837	815
Separate accounts taxable fixed maturities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	0	0
Separate accounts taxable fixed maturities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	837	815
Separate accounts taxable fixed maturities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	$ 0	$ 0