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Fair Value Measurements (Details) - Fair Value Hierarchy - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2025 | Dec. 31, 2024
Corporate and all other bonds [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Transfers into Level 3 | $ 133 |
Recurring basis [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 91,827 | $ 84,373
Recurring basis [Member] | Fixed maturities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 91,113 | 83,666
Recurring basis [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 4,013 | 5,570
Recurring basis [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 30,304 | 27,185
Recurring basis [Member] | Debt securities issued by foreign governments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 988 | 909
Recurring basis [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 13,361 | 12,605
Recurring basis [Member] | Corporate and all other bonds [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 42,447 | 37,397
Recurring basis [Member] | Equity securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 692 | 687
Recurring basis [Member] | Common stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 649 | 639
Recurring basis [Member] | Non-redeemable preferred stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 43 | 48
Recurring basis [Member] | Other Investments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 22 | 20
Recurring basis [Member] | Level 1 [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 4,706 | 6,237
Recurring basis [Member] | Level 1 [Member] | Fixed maturities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 4,026 | 5,570
Recurring basis [Member] | Level 1 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 4,013 | 5,570
Recurring basis [Member] | Level 1 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 1 [Member] | Debt securities issued by foreign governments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 1 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 1 [Member] | Corporate and all other bonds [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 13 | 0
Recurring basis [Member] | Level 1 [Member] | Equity securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 658 | 647
Recurring basis [Member] | Level 1 [Member] | Common stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 642 | 631
Recurring basis [Member] | Level 1 [Member] | Non-redeemable preferred stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 16 | 16
Recurring basis [Member] | Level 1 [Member] | Other Investments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 22 | 20
Recurring basis [Member] | Level 2 [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 86,751 | 77,850
Recurring basis [Member] | Level 2 [Member] | Fixed maturities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 86,748 | 77,847
Recurring basis [Member] | Level 2 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 2 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 30,304 | 27,185
Recurring basis [Member] | Level 2 [Member] | Debt securities issued by foreign governments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 988 | 909
Recurring basis [Member] | Level 2 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 13,358 | 12,602
Recurring basis [Member] | Level 2 [Member] | Corporate and all other bonds [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 42,098 | 37,151
Recurring basis [Member] | Level 2 [Member] | Equity securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 3 | 3
Recurring basis [Member] | Level 2 [Member] | Common stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 2 [Member] | Non-redeemable preferred stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 3 | 3
Recurring basis [Member] | Level 2 [Member] | Other Investments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 3 [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 370 | 286
Recurring basis [Member] | Level 3 [Member] | Fixed maturities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 339 | 249
Recurring basis [Member] | Level 3 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 3 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 3 [Member] | Debt securities issued by foreign governments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 0 | 0
Recurring basis [Member] | Level 3 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 3 | 3
Recurring basis [Member] | Level 3 [Member] | Corporate and all other bonds [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 336 | 246
Recurring basis [Member] | Level 3 [Member] | Equity securities [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 31 | 37
Recurring basis [Member] | Level 3 [Member] | Common stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 7 | 8
Recurring basis [Member] | Level 3 [Member] | Non-redeemable preferred stock [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 24 | 29
Recurring basis [Member] | Level 3 [Member] | Investment in non-public common and preferred equity securities where the fair value estimate is determined either internally or by an external fund manager [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | 31 | 37
Recurring basis [Member] | Level 3 [Member] | Other Investments [Member] |  |
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured |  |
Total invested assets measured on a recurring basis | $ 0 | $ 0

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