Investments and Cash - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Investment Income
Gross investment income	$ 274	$ 275	$ 304
Investment expenses	(5)	(6)	(7)
Net investment income	269	269	297
Fair value gains (losses) on trading securities	(34)	0	0
Equity in earnings (losses) of investees	(39)	94	27
Fair value loss on trading securities still held	29
Externally managed
Net Investment Income
Gross investment income	189	204	231
Loss Mitigation Securities and other
Net Investment Income
Gross investment income	63	55	65
AssuredIM Funds
Net Investment Income
Gross investment income	$ 22	$ 16	$ 8

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 unrealized gain (loss) recognized in income from asset (liability) measured at fair value on recurring basis using unobservable input (level 3) and still held.

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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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