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Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2024 | Dec. 31, 2023 | Jun. 30, 2023
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | $ 1,159 | $ 1,032 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3 | 3 | $ 1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 45 | 40 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 372 | 187 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 5 | 4 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 787 | 844 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 71 | 68 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 78 | 71 |
Fixed maturity securities, at fair value | 2,043 |  |
Debt Securities, Available-for-sale, Amortized Cost | 2,078 | 2,197 |
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease) | 0 |  |
Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 46 | 4 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 46 | 4 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Fixed maturity securities, at fair value | 314 | 426 |
Debt Securities, Available-for-sale, Amortized Cost | 314 | 426 |
Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 1,113 | 1,028 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3 | 3 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 45 | 40 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 326 | 184 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 5 | 4 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 787 | 844 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 71 | 68 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 77 | 71 |
Fixed maturity securities, at fair value | 1,703 | 1,710 |
Debt Securities, Available-for-sale, Amortized Cost | 1,737 | 1,744 |
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 35 | 23 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 21 | 7 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 15 | 16 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 1 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 2 | 1 |
Fixed maturity securities, at fair value | 71 | 72 |
Debt Securities, Available-for-sale, Amortized Cost | 71 | 72 |
Fixed Income Securities [Member] | Corporate Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 618 | 584 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 2 | 4 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 125 | 75 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 3 | 2 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 493 | 509 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 43 | 43 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 46 | 44 |
Fixed maturity securities, at fair value | 742 | 745 |
Debt Securities, Available-for-sale, Amortized Cost | 786 | 785 |
Fixed Income Securities [Member] | Foreign Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 80 | 64 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 25 | 8 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 55 | 56 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 7 | 6 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 7 | 6 |
Fixed maturity securities, at fair value | 105 | 100 |
Debt Securities, Available-for-sale, Amortized Cost | 111 | 105 |
Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 95 | 63 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 58 | 27 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 37 | 37 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 3 | 2 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 4 | 4 |
Fixed maturity securities, at fair value | 105 | 82 |
Debt Securities, Available-for-sale, Amortized Cost | 108 | 85 |
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 129 | 104 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3 | 3 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 28 | 28 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 16 | 6 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 113 | 98 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 13 | 14 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 13 | 14 |
Fixed maturity securities, at fair value | 253 | 250 |
Debt Securities, Available-for-sale, Amortized Cost | 240 | 239 |
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 22 | 95 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 18 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 3 | 93 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 1 |
Fixed maturity securities, at fair value | 141 | 139 |
Debt Securities, Available-for-sale, Amortized Cost | 141 | 139 |
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 117 | 92 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 12 | 3 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 45 | 57 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 1 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 72 | 35 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 4 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 5 | 1 |
Fixed maturity securities, at fair value | 241 | 303 |
Debt Securities, Available-for-sale, Amortized Cost | 234 | 301 |
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 17 | 3 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 17 | 3 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Fixed maturity securities, at fair value | 46 |  |
Debt Securities, Available-for-sale, Amortized Cost | 46 |  |
Fixed Income Securities [Member] | Collateralized Mortgage Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Fixed maturity securities, at fair value | 46 | 19 |
Debt Securities, Available-for-sale, Amortized Cost | 46 | 19 |
Fixed Income Investments And Other Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3 | 3 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 45 | 40 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 77 | 71 |
Fixed maturity securities, at fair value | 2,017 | 2,135 |
Debt Securities, Available-for-sale, Amortized Cost | 2,051 | 2,170 |
Collateral Pledged [Member] | Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 1 | 0 |
Fixed maturity securities, at fair value | 25 | 27 |
Debt Securities, Available-for-sale, Amortized Cost | 27 | 0 |
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Fixed maturity securities, at fair value | 0 | 27 |
Debt Securities, Available-for-sale, Amortized Cost | 0 | 27 |
Collateral Pledged [Member] | Fixed Income Securities [Member] | US Treasury and Government |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 1 | 0 |
Fixed maturity securities, at fair value | 25 | 0 |
Debt Securities, Available-for-sale, Amortized Cost | 27 | 0 |
Asset Pledged as Collateral [Member] | Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Amortized Cost | $ 27 | $ 27 |

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