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
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