Fair Value Measurements - Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	$ 11,734	$ 13,022
Separate accounts	888	959
Top Hat savings plan mutual funds and common equity (included in Other assets)	51	64
Fair value of asset	21,436	25,349
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	6,679	7,497
States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	4,482	5,095
Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	240	273
United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	188	123
Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	119	8
Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	26	26
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	188	123
Top Hat savings plan mutual funds and common equity (included in Other assets)	51	64
Fair value of asset	8,672	11,049
Quoted prices in active markets for identical assets (Level 1) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Quoted prices in active markets for identical assets (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
Quoted prices in active markets for identical assets (Level 1) | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	188	123
Quoted prices in active markets for identical assets (Level 1) | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	11,546	12,899
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Fair value of asset	12,764	14,300
Significant other observable inputs (Level 2) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	6,679	7,497
Significant other observable inputs (Level 2) | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	4,482	5,095
Significant other observable inputs (Level 2) | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	240	273
Significant other observable inputs (Level 2) | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant other observable inputs (Level 2) | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	119	8
Significant other observable inputs (Level 2) | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	26	26
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Fair value of asset	0	0
Significant unobservable inputs (Level 3) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant unobservable inputs (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
Significant unobservable inputs (Level 3) | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant unobservable inputs (Level 3) | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant unobservable inputs (Level 3) | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Significant unobservable inputs (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	8,433	10,862
Equity securities | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	407	453
Equity securities | Quoted prices in active markets for identical assets (Level 1) | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	8,433	10,862
Equity securities | Quoted prices in active markets for identical assets (Level 1) | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Significant other observable inputs (Level 2) | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Significant other observable inputs (Level 2) | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	407	453
Equity securities | Significant unobservable inputs (Level 3) | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Equity securities | Significant unobservable inputs (Level 3) | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	0	0
Taxable Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	811	948
Taxable Fixed Maturities | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	0	0
Taxable Fixed Maturities | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	811	948
Taxable Fixed Maturities | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	$ 0	$ 0