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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 | Jun. 30, 2022 | Dec. 31, 2021 | Jun. 30, 2021
--- | --- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | $ 1,228 | $ 810 |
Debt Securities, Available-for-sale, Amortized Cost | 1,979 | 2,140 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 | $ 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 39 | 141 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 1,041 | 768 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 48 | 14 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 186 | 41 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 23 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 71 | 16 |
Available-for-sale Securities, Current | 1,947 | 2,265 |
Fixed maturity securities, at fair value | 1,947 |  |
Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 191 | 128 |
Debt Securities, Available-for-sale, Amortized Cost | 452 | 415 |
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 | 181 | 114 |
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 | 10 | 13 |
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 | 452 | 414 |
Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 1,037 | 682 |
Debt Securities, Available-for-sale, Amortized Cost | 1,442 | 1,605 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 39 | 141 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 861 | 654 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 48 | 14 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 177 | 28 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 23 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 71 | 16 |
Fixed maturity securities, at fair value | 1,410 | 1,730 |
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 18 | 118 |
Debt Securities, Available-for-sale, Amortized Cost | 55 | 315 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4 | 28 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 17 | 117 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 3 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 1 | 2 |
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 | 1 | 3 |
Fixed maturity securities, at fair value | 58 | 340 |
Fixed Income Securities [Member] | Corporate Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 606 | 380 |
Debt Securities, Available-for-sale, Amortized Cost | 695 | 612 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1 | 10 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 489 | 363 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 33 | 8 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 117 | 17 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 19 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 52 | 9 |
Fixed maturity securities, at fair value | 644 | 613 |
Fixed Income Securities [Member] | Foreign Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 80 | 78 |
Debt Securities, Available-for-sale, Amortized Cost | 86 | 89 |
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 | 38 | 75 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 2 | 2 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 42 | 3 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 3 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 5 | 2 |
Fixed maturity securities, at fair value | 81 | 87 |
Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 42 | 27 |
Debt Securities, Available-for-sale, Amortized Cost | 63 | 45 |
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 | 38 | 25 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 4 | 2 |
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 | 2 | 1 |
Fixed maturity securities, at fair value | 62 | 45 |
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 101 | 2 |
Debt Securities, Available-for-sale, Amortized Cost | 176 | 182 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 27 | 70 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 100 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 5 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 1 | 1 |
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 | 5 | 0 |
Fixed maturity securities, at fair value | 197 | 252 |
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 130 | 71 |
Debt Securities, Available-for-sale, Amortized Cost | 137 | 128 |
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 | 120 | 68 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 4 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 11 | 3 |
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 | 5 | 0 |
Fixed maturity securities, at fair value | 132 | 128 |
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 60 | 6 |
Debt Securities, Available-for-sale, Amortized Cost | 230 | 234 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 6 | 32 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 60 | 6 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 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 | 1 | 0 |
Fixed maturity securities, at fair value | 236 | 265 |
Fixed Income Investments And Other Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 1,895 | 2,020 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 39 | 141 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 71 | 16 |
Fixed maturity securities, at fair value | 1,862 | 2,145 |
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 | 0 | 0 |
Fixed maturity securities, at fair value | 85 | 120 |
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 70 | 105 |
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 | 70 | 105 |
Collateral Pledged [Member] | Fixed Income Securities [Member] | US Treasury and Government |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 15 | 15 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0 |
Fixed maturity securities, at fair value | 15 | 15 |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Asset Pledged as Collateral [Member] | Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 85 | 120 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | $ 0 | $ 0 |

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