| **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           |

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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| - Definition
Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.
+ References
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| - Definition
Value of the other investment not readily marketable determined by management based upon fair value methods, including pricing of similar securities and valuation techniques, that was used to record the investment for financial reporting purposes.
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| - Definition
Amount of asset at fair value held for benefit of separate account policyholder.
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