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Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
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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 |  | $ 6,994 | $ 7,188
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 |  | 4,507 | 5,145
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 |  | 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) | 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 | U.S. government and government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 4,507 | 5,145
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 | 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) | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,599 | 1,198
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 |  | 876 | 829
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 |  | 12 | 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 |  | 8 | 5
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 | 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) | Fair value option | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1 | 1
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 | 10
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 |  | 17,972 | 15,474
Liabilities measured at fair value |  | (62) | (76)
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 |  | (62) | (76)
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 |  | 2 | 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 |  | 16,827 | 14,417
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 |  | 9,877 | 7,899
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 |  | 860 | 795
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 |  | 306 | 419
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 |  | 1,082 | 1,047
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 |  | 22 | 17
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 |  | 2,277 | 2,313
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 |  | 2,403 | 1,927
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 |  | 103 | 134
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 |  | 30 | 28
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 |  | 125 | 149
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 |  | 885 | 744
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 |  | 639 | 543
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 | Non-U.S. government securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 10 | 4
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 | 2
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 |  | 7 | 32
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 |  | 227 | 163
Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 195 | 161
Liabilities measured at fair value |  | (19) | (14)
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 |  | (19) | (14)
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 |  | 100 | 121
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 |  | 100 | 121
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) | 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 | 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 | 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 | 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) | Short-term investments |  |  |
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) | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 5 | 3
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 |  | 90 | 37
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 | 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 | 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) | Fair value option | Short-term investments |  |  |
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 | 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 |  | 86 | 33
Estimated Fair Value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 26,020 | 23,670
Liabilities measured at fair value |  | (81) | (90)
Estimated Fair Value | Other liabilities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (19) | (14)
Estimated Fair Value | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities measured at fair value |  | (62) | (76)
Estimated Fair Value | Residential mortgage loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 2 | 2
Estimated Fair Value | Fixed maturities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 21,434 | 19,683
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 |  | 9,977 | 8,020
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 |  | 860 | 795
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 |  | 306 | 419
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 |  | 1,082 | 1,047
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 |  | 4,529 | 5,162
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 |  | 2,277 | 2,313
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 |  | 2,403 | 1,927
Estimated Fair Value | Short-term investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,702 | 1,332
Estimated Fair Value | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 911 | 860
Estimated Fair Value | Derivative instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 125 | 149
Estimated Fair Value | Fair value option |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets measured at fair value |  | 1,846 | 1,644
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 |  | 639 | 543
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 |  | 8 | 5
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 |  | 10 | 4
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 | 2
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 |  | 8 | 33
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 | 14
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 |  | 313 | 196
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] | $ 859 | $ 847
[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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