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Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021
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Standard & Poor's, B Rating [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | $ 451 | $ 757
Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 451 | 754
Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors |  | 2
Standard & Poor's, C Rating | Assured Guaranty Municipal Corporation |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors |  | 1
Standard & Poor's, A Rating | Assured Guaranty Municipal Corporation |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 1 |
Municipal Bonds [Member] | Standard & Poor's, B Rating [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 48 | 318
Municipal Bonds [Member] | Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 47 | 316
Municipal Bonds [Member] | Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors |  | 2
Municipal Bonds [Member] | Standard & Poor's, C Rating | Assured Guaranty Municipal Corporation |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors |  | 1
Municipal Bonds [Member] | Standard & Poor's, A Rating | Assured Guaranty Municipal Corporation |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 1 |
Mortgage And Other Asset Backed Securities [Member] | Standard & Poor's, B Rating [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 403 | 439
Mortgage And Other Asset Backed Securities [Member] | Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | $ 403 | $ 439

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