Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail2) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Investment [Line Items]
Securities fair value	$ 23	$ 17
Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Securities Pledged to Derivative Counterparties	64	120
Standard & Poor's, B Rating
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	403
Standard & Poor's, B Rating | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	403
Standard & Poor's, B Rating | Municipal Bonds [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	10
Standard & Poor's, B Rating | Municipal Bonds [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	10
Standard & Poor's, B Rating | Corporate Debt Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0
Standard & Poor's, B Rating | Mortgage and Asset-Backed Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	394
Standard & Poor's, B Rating | Mortgage and Asset-Backed Securities [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 394
Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		2
Standard & Poor's, BBB- Rating [Member] | Municipal Bonds [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		2
Standard & Poor's, BBB- Rating [Member] | Corporate Debt Securities [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		0
Standard & Poor's, C Rating | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		1
Standard & Poor's, C Rating | Municipal Bonds [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		1
Standard & Poor's, C Rating | Corporate Debt Securities [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		0
Standard & Poor's, CCC+ Rating
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		757
Standard & Poor's, CCC+ Rating | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		754
Standard & Poor's, CCC+ Rating | Municipal Bonds [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		318
Standard & Poor's, CCC+ Rating | Municipal Bonds [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		316
Standard & Poor's, CCC+ Rating | Corporate Debt Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		0
Standard & Poor's, CCC+ Rating | Mortgage and Asset-Backed Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		439
Standard & Poor's, CCC+ Rating | Mortgage and Asset-Backed Securities [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		$ 439