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Investments - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions | Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023 | Jun. 30, 2023 | Mar. 31, 2023 | Dec. 31, 2022
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Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 100.00% |  | 100.00% |  |  |
Amortized Cost | $ 6,478 |  | $ 6,746 |  |  |
Allowance for Credit Losses | (69) | $ (67) | (77) | $ (79) | $ (69) | $ (65)
Gross Unrealized Gains | 38 |  | 55 |  |  |
Gross Unrealized Losses | (441) |  | (417) |  |  |
Estimated Fair Value | $ 6,006 |  | $ 6,307 |  |  |
Government agency obligations as a percentage of total mortgage backed securities | 61.00% |  | 42.00% |  |  |
Obligations of state and political subdivisions |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 35.00% |  | 41.00% |  |  |
Amortized Cost | $ 2,239 |  | $ 2,733 |  |  |
Allowance for Credit Losses | (14) |  | (13) |  |  |
Gross Unrealized Gains | 25 |  | 33 |  |  |
Gross Unrealized Losses | (105) |  | (92) |  |  |
Estimated Fair Value | $ 2,145 |  | $ 2,661 |  |  |
U.S. government and agencies |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 1.00% |  | 1.00% |  |  |
Amortized Cost | $ 77 |  | $ 65 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 1 |  | 1 |  |  |
Gross Unrealized Losses | (6) |  | (6) |  |  |
Estimated Fair Value | $ 72 |  | $ 60 |  |  |
Corporate securities |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 37.00% |  | 34.00% |  |  |
Amortized Cost | $ 2,358 |  | $ 2,327 |  |  |
Allowance for Credit Losses | (6) |  | (6) |  |  |
Gross Unrealized Gains | 8 |  | 17 |  |  |
Gross Unrealized Losses | (214) |  | (197) |  |  |
Estimated Fair Value | $ 2,146 |  | $ 2,141 |  |  |
RMBS |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 9.00% |  | 6.00% |  |  |
Amortized Cost | $ 565 |  | $ 428 |  |  |
Allowance for Credit Losses | (21) |  | (21) |  |  |
Gross Unrealized Gains | 2 |  | 3 |  |  |
Gross Unrealized Losses | (69) |  | (68) |  |  |
Estimated Fair Value | $ 477 |  | $ 342 |  |  |
CMBS |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 3.00% |  | 2.00% |  |  |
Amortized Cost | $ 204 |  | $ 157 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized Losses | (6) |  | (6) |  |  |
Estimated Fair Value | $ 198 |  | $ 151 |  |  |
CLOs |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 6.00% |  | 7.00% |  |  |
Amortized Cost | $ 412 |  | $ 456 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 1 |  | 1 |  |  |
Gross Unrealized Losses | (2) |  | (7) |  |  |
Estimated Fair Value | $ 411 |  | $ 450 |  |  |
Others |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 8.00% |  | 7.00% |  |  |
Amortized Cost | $ 538 |  | $ 465 |  |  |
Allowance for Credit Losses | (28) |  | (37) |  |  |
Gross Unrealized Gains | 1 |  | 0 |  |  |
Gross Unrealized Losses | (24) |  | (26) |  |  |
Estimated Fair Value | $ 487 |  | $ 402 |  |  |
Non-U.S. government securities |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |
Percent of Total | 1.00% |  | 2.00% |  |  |
Amortized Cost | $ 85 |  | $ 115 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized Losses | (15) |  | (15) |  |  |
Estimated Fair Value | $ 70 |  | $ 100 |  |  |

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