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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 | Mar. 31, 2022 | Dec. 31, 2021 | Mar. 31, 2021
--- | --- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | $ 794 | $ 810 |
Debt Securities, Available-for-sale, Amortized Cost | 2,006 | 2,140 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 1 | 0 | $ 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 73 | 141 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 598 | 768 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 26 | 14 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 196 | 41 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 17 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 43 | 16 |
Available-for-sale Securities, Current | 2,036 | 2,265 |
Fixed maturity securities, at fair value | 2,036 |  |
Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 30 | 128 |
Debt Securities, Available-for-sale, Amortized Cost | 540 | 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 | 18 | 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 | 12 | 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 | 540 | 414 |
Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 764 | 682 |
Debt Securities, Available-for-sale, Amortized Cost | 1,352 | 1,605 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 1 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 73 | 141 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 580 | 654 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 26 | 14 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 184 | 28 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 16 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 42 | 16 |
Fixed maturity securities, at fair value | 1,383 | 1,730 |
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 19 | 118 |
Debt Securities, Available-for-sale, Amortized Cost | 65 | 315 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 5 | 28 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 19 | 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 | 69 | 340 |
Fixed Income Securities [Member] | Corporate Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 466 | 380 |
Debt Securities, Available-for-sale, Amortized Cost | 610 | 612 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 1 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 2 | 10 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 349 | 363 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 21 | 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 | 13 | 1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 34 | 9 |
Fixed maturity securities, at fair value | 577 | 613 |
Fixed Income Securities [Member] | Foreign Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 87 | 78 |
Debt Securities, Available-for-sale, Amortized Cost | 92 | 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 | 36 | 75 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 1 | 2 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 51 | 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 | 4 | 2 |
Fixed maturity securities, at fair value | 88 | 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 | 49 | 27 |
Debt Securities, Available-for-sale, Amortized Cost | 53 | 45 |
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 | 44 | 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 | 5 | 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 | 51 | 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 | 17 | 2 |
Debt Securities, Available-for-sale, Amortized Cost | 179 | 182 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 47 | 70 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 16 | 0 |
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 | 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 | 0 | 0 |
Fixed maturity securities, at fair value | 225 | 252 |
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 120 | 71 |
Debt Securities, Available-for-sale, Amortized Cost | 121 | 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 | 111 | 68 |
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 | 9 | 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 | 1 | 0 |
Fixed maturity securities, at fair value | 120 | 128 |
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position | 6 | 6 |
Debt Securities, Available-for-sale, Amortized Cost | 232 | 234 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 20 | 32 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 6 | 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 | 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 | 252 | 265 |
Fixed Income Investments And Other Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 1,892 | 2,020 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 1 | 0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 73 | 141 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 42 | 16 |
Fixed maturity securities, at fair value | 1,922 | 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 | 114 | 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 | 99 | 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 | 99 | 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 | 114 | 120 |
Debt Securities, Available-for-sale, Allowance for Credit Loss | $ 0 | $ 0 |

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