v3.25.3
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