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Fair Value Measurements - Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | $ 17,630 | $ 16,182
Fair value of asset | 31,338 | 28,628
Separate accounts | 971 | 952
Short-Term Investments | 149 | 298
Top Hat savings plan mutual funds and common equity (included in Other assets) | 100 | 87
Corporate |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 9,363 | 8,380
States, municipalities and political subdivisions |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 4,846 | 4,721
Government-sponsored enterprises |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 2,346 | 2,274
Asset-backed |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 778 | 551
United States government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 274 | 226
Foreign government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 23 | 30
Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 274 | 226
Fair value of asset | 12,767 | 11,447
Short-Term Investments | 149 | 298
Top Hat savings plan mutual funds and common equity (included in Other assets) | 100 | 87
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 | Asset-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 | 274 | 226
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 | 17,356 | 15,956
Fair value of asset | 18,571 | 17,181
Short-Term Investments | 0 | 0
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 | 9,363 | 8,380
Level 2 | States, municipalities and political subdivisions |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 4,846 | 4,721
Level 2 | Government-sponsored enterprises |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 2,346 | 2,274
Level 2 | Asset-backed |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fixed maturities, at fair value | 778 | 551
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 | 23 | 30
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
Short-Term Investments | 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 | Asset-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 | 12,209 | 10,836
Equity securities | Nonredeemable preferred equities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fair value of asset | 338 | 349
Equity securities | Level 1 | Common equities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Fair value of asset | 12,209 | 10,836
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 | 338 | 349
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 | 912 | 876
Separate accounts taxable fixed maturities | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Separate accounts | 35 | 0
Separate accounts taxable fixed maturities | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Separate accounts | 877 | 876
Separate accounts taxable fixed maturities | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |
Separate accounts | $ 0 | $ 0

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