Long-Term Debt and Credit Facilities - Principal and Carrying Amounts of Debt (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Sep. 27, 2021	Aug. 20, 2021	May 26, 2021	Jun. 20, 2014	Nov. 22, 2006	May 18, 2004
Debt Instrument [Line Items]
Carrying Value	$ (1,675,000,000)	$ (1,673,000,000)
Assured Guaranty Municipal Corp
Debt Instrument [Line Items]
Principal	1,726,000,000	1,728,000,000
Carrying Value	$ (1,675,000,000)	(1,673,000,000)
Senior Notes | AGC | 7% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)	700.00%							700.00%
Principal	$ 200,000,000	200,000,000						$ 200,000,000
Carrying Value	$ (198,000,000)	(197,000,000)
Senior Notes | AGC | 5% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)	5.00%					5.00%
Principal	$ 330,000,000	330,000,000	$ 500,000,000			$ 500,000,000
Carrying Value	$ (329,000,000)	(329,000,000)
Senior Notes | AGC | 3.15% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)	3.15%
Principal	$ 500,000,000	500,000,000			$ 500,000,000
Carrying Value	$ (495,000,000)	(495,000,000)
Senior Notes | AGC | 3.6% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)	3.60%
Principal	$ 400,000,000	400,000,000		$ 400,000,000
Carrying Value	(395,000,000)	(395,000,000)
Senior Notes | AGMH | 3.15% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)					3.15%
Senior Notes | AGMH | 3.6% Senior Notes
Debt Instrument [Line Items]
Interest rate of debt (as a percent)				3.60%
Enhanced Junior Subordinated Debentures | AGC
Debt Instrument [Line Items]
Principal	150,000,000	150,000,000
Carrying Value	(150,000,000)	(150,000,000)
Junior Subordinated Debentures | AGMH
Debt Instrument [Line Items]
Principal	146,000,000	146,000,000					$ 300,000,000
Carrying Value	(108,000,000)	(105,000,000)
Notes Payable, Other Payables | Assured Guaranty Municipal Corp
Debt Instrument [Line Items]
Principal	0	2,000,000
Carrying Value	$ 0	$ (2,000,000)