Investments - Net Investment Income and Equity in Earnings of Investees (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Net Investment Income
Gross investment income	$ 63	$ 71
Investment expenses	(1)	(1)
Net investment income	62	70
Unrealized gain (loss) on trading securities	(4)	0
Segment equity in earnings (losses) of investees	(11)	9
Fair Value Measured at Net Asset Value Per Share
Net Investment Income
Segment equity in earnings (losses) of investees	3
Dividends received	5
Externally managed
Net Investment Income
Gross investment income	48	51
Loss mitigation securities and other
Net Investment Income
Gross investment income	11	16
AssuredIM managed fixed-maturity securities
Net Investment Income
Gross investment income	$ 4	$ 4

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of dividend income on investment in equity security, classified as operating.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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