Investments and Cash - Narrative (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) manager Security	Dec. 31, 2021 USD ($) Security	Dec. 31, 2020 USD ($)
Schedule of Cost-method Investments [Line Items]
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Fair value gains (losses) on trading securities
Number of investment portfolio managers | manager	3
Accrued investment income	$ 71,000,000	$ 69,000,000
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | Security	567	23
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 329,000,000	$ 6,000,000
Assets held-in-trust	222,000,000	243,000,000
Non-income producing investments	0	0
Credit loss expense	21,000,000	7,000,000	$ 17,000,000
Purchased with credit deterioration, amount at purchase price	22,000,000
Securities purchased with credit deterioration, amount at par value	31,000,000
Allowance for credit loss at acquisition date	2,000,000
Discount attributable to other factors	7,000,000
PCI Securities
Schedule of Cost-method Investments [Line Items]
Credit loss expense	21,000,000	6,000,000	16,000,000
Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Assets held-in-trust	1,169,000,000	1,231,000,000
Future Equity Investments
Schedule of Cost-method Investments [Line Items]
Purchase commitment, remaining minimum amount committed	78,000,000
AssuredIM Funds | Equity in Earnings (Losses) of Investees | Assured Guaranty Asset Strategies LLC
Schedule of Cost-method Investments [Line Items]
Fair value of investment	569,000,000	543,000,000
AssuredIM Funds | Equity in Earnings (Losses) of Investees | Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Long-term purchase commitment, amount	755,000,000
AssuredIM Funds | Future Equity Investments | Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Authorized amount to invest	750,000,000
Investments, including distributed gains, authorized amount to invest	810,000,000
AssuredIM Funds | Invested Capital | Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Long-term purchase commitment, amount	536,000,000
AssuredIM Funds | Unfunded Commitment | Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Long-term purchase commitment, amount	219,000,000
Equity Securities
Schedule of Cost-method Investments [Line Items]
Cash dividends from subsidiaries	$ 10,000,000	$ 15,000,000	$ 10,000,000