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Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | $ 10,533 | $ 8,745
Liabilities measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other liabilities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 5,852 | 5,792
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 5,850 | 5,792
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Commercial mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Residential mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 3,081 | 1,786
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,590 | 1,151
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 10 | 16
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 4 | 13
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  |  | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Short term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 3 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 3 | 3
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Other investments fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Other Observable Inputs (Level 2) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 24,340 | 18,927
Liabilities measured at fair value |  | (81) | (119)
Significant Other Observable Inputs (Level 2) | Other liabilities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | 0 | 0
Significant Other Observable Inputs (Level 2) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (81) | (119)
Significant Other Observable Inputs (Level 2) | Residential mortgage loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 13 | 2
Significant Other Observable Inputs (Level 2) | Fixed maturities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 22,441 | 17,614
Significant Other Observable Inputs (Level 2) | Fixed maturities | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 13,853 | 10,708
Significant Other Observable Inputs (Level 2) | Fixed maturities | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 13 | 22
Significant Other Observable Inputs (Level 2) | Fixed maturities | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2,989 | 2,250
Significant Other Observable Inputs (Level 2) | Fixed maturities | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2,853 | 2,062
Significant Other Observable Inputs (Level 2) | Fixed maturities | Commercial mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,146 | 1,213
Significant Other Observable Inputs (Level 2) | Fixed maturities | Residential mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,313 | 1,103
Significant Other Observable Inputs (Level 2) | Fixed maturities | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 274 | 256
Significant Other Observable Inputs (Level 2) | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 163 | 193
Significant Other Observable Inputs (Level 2) | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 27 | 30
Significant Other Observable Inputs (Level 2) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 147 | 197
Significant Other Observable Inputs (Level 2) | Fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,549 | 891
Significant Other Observable Inputs (Level 2) | Fair value option | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,085 | 662
Significant Other Observable Inputs (Level 2) | Fair value option | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Other Observable Inputs (Level 2) | Fair value option | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  |  | 2
Significant Other Observable Inputs (Level 2) | Fair value option | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 8 | 6
Significant Other Observable Inputs (Level 2) | Fair value option | Short term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 43 | 11
Significant Other Observable Inputs (Level 2) | Fair value option | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Other Observable Inputs (Level 2) | Fair value option | Other investments fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 413 | 210
Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 553 | 356
Liabilities measured at fair value |  | (43) | (22)
Significant Unobservable Inputs (Level 3) | Other liabilities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (43) | (22)
Significant Unobservable Inputs (Level 3) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Residential mortgage loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 141 | 147
Significant Unobservable Inputs (Level 3) | Fixed maturities | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 141 | 147
Significant Unobservable Inputs (Level 3) | Fixed maturities | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Commercial mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Residential mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 97 | 84
Significant Unobservable Inputs (Level 3) | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 6 | 5
Significant Unobservable Inputs (Level 3) | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 309 | 120
Significant Unobservable Inputs (Level 3) | Fair value option | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fair value option | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fair value option | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  |  | 0
Significant Unobservable Inputs (Level 3) | Fair value option | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 0 | 0
Significant Unobservable Inputs (Level 3) | Fair value option | Short term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 15 | 10
Significant Unobservable Inputs (Level 3) | Fair value option | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 4 | 4
Significant Unobservable Inputs (Level 3) | Fair value option | Other investments fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 290 | 106
Estimated Fair Value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 36,819 | 29,489
Liabilities measured at fair value |  | (124) | (141)
Estimated Fair Value | Other liabilities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (43) | (22)
Estimated Fair Value | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (81) | (119)
Estimated Fair Value | Residential mortgage loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 13 | 2
Estimated Fair Value | Fixed maturities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 28,434 | 23,553
Estimated Fair Value | Fixed maturities | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 13,996 | 10,855
Estimated Fair Value | Fixed maturities | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 5,863 | 5,814
Estimated Fair Value | Fixed maturities | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2,989 | 2,250
Estimated Fair Value | Fixed maturities | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2,853 | 2,062
Estimated Fair Value | Fixed maturities | Commercial mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,146 | 1,213
Estimated Fair Value | Fixed maturities | Residential mortgage backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,313 | 1,103
Estimated Fair Value | Fixed maturities | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 274 | 256
Estimated Fair Value | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 3,341 | 2,063
Estimated Fair Value | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,623 | 1,186
Estimated Fair Value | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 147 | 197
Estimated Fair Value | Fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 3,261 | 2,488
Estimated Fair Value | Fair value option | Corporate bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,085 | 662
Estimated Fair Value | Fair value option | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 4 | 13
Estimated Fair Value | Fair value option | Asset backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  |  | 2
Estimated Fair Value | Fair value option | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 8 | 6
Estimated Fair Value | Fair value option | Short term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 61 | 21
Estimated Fair Value | Fair value option | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 7 | 7
Estimated Fair Value | Fair value option | Other investments fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 703 | 316
Estimated Fair Value | Fair value option | Other investments measured at net asset value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value | [1] | $ 1,393 | $ 1,461
[1] | In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

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