Fair Value Measurements - Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	$ 12,376	$ 13,022
Separate accounts	903	959
Top Hat savings plan mutual funds and common equity (included in Other assets)	70	64
Fair value of asset	24,008	25,349
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	70	64
Fair value of asset	10,427	11,049
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Fair value of asset	13,581	14,300
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Fair value of asset	0	0
Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	12,376	13,022
Debt Securities | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	7,149	7,497
Debt Securities | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	4,810	5,095
Debt Securities | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	266	273
Debt Securities | United States government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	112	123
Debt Securities | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	25	26
Debt Securities | Government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	14	8
Debt Securities | 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	112	123
Debt Securities | 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
Debt Securities | 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
Debt Securities | 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
Debt Securities | 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	112	123
Debt Securities | 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
Debt Securities | 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
Debt Securities | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	12,264	12,899
Debt Securities | Significant other observable inputs (Level 2) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	7,149	7,497
Debt Securities | 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	4,810	5,095
Debt Securities | 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	266	273
Debt Securities | 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
Debt Securities | Significant other observable inputs (Level 2) | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	25	26
Debt Securities | 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	14	8
Debt Securities | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Debt Securities | Significant unobservable inputs (Level 3) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fixed maturities, at fair value	0	0
Debt Securities | 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
Debt Securities | 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
Debt Securities | 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
Debt Securities | 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
Debt Securities | 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
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	10,245	10,862
Equity securities | Nonredeemable preferred equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of asset	430	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	10,245	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	430	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	887	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	887	948
Taxable Fixed Maturities | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Separate accounts	$ 0	$ 0