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Fair Value Measurements - Additional Information (Details) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities | $ 283,000 | $ 19,000
Derivative liabilities | $ 86,000,000 | $ 114,000,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs | 2.20% | 2.20%
Variable Interest Entity, Primary Beneficiary [Member] |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Derivative liabilities | $ 1,739,000,000 | $ 1,835,000,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs | 2.80% | 2.40%
Fair Value Measured at Net Asset Value Per Share [Member] |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Other investments | $ 501,000,000 | $ 453,000,000
Fixed Income Securities [Member] |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Percentage of investment portfolio valued using dealer quotes | 3.00% | 2.00%
Minimum [Member] | Fixed Income Securities [Member] |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Percentage of investment portfolio valued using internal valuation models | 2.00% | 3.00%
Maximum [Member] | Fixed Income Securities [Member] |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Percentage of investment portfolio valued using external pricing services | 95.00% | 95.00%
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Note Holders | 1 |
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 | Corolla Notes |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |
Note Holders | 1 |

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