Investments - Net Investment Income and Equity in Earnings of Investees (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Investment Income
Gross investment income	$ 67	$ 73	$ 208	$ 235
Investment expenses	(1)	(2)	(4)	(6)
Net investment income	66	71	204	229
Equity in earnings of investees	23	7	66	3
Fair Value Measured at Net Asset Value Per Share
Net Investment Income
Equity in earnings of investees	13		39
Externally managed
Net Investment Income
Gross investment income	52	54	155	178
Loss mitigation securities and other
Net Investment Income
Gross investment income	11	16	41	53
AssuredIM managed fixed-maturity securities
Net Investment Income
Gross investment income	$ 4	$ 3	$ 12	$ 4

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

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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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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