Long-Term Debt and Credit Facilities - Narrative (Details)											12 Months Ended
	Mar. 14, 2022 USD ($)	Feb. 03, 2022 USD ($)	Sep. 27, 2021 USD ($)	Aug. 20, 2021 USD ($)	Jul. 09, 2021 USD ($)	May 26, 2021 USD ($)	Jun. 20, 2014 USD ($)	Dec. 20, 2006 USD ($) period	Nov. 22, 2006 USD ($) rISK extension	May 18, 2004 USD ($)	Dec. 31, 2022 USD ($) Trust	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 31, 2003	Nov. 26, 2002
Debt Instrument [Line Items]
Net proceeds from issuance of debt											$ 0	$ 889,000,000	$ 0
Repayments of long-term debt											2,000,000	620,000,000	22,000,000
Loss on extinguishment of debt											0	175,000,000	0
Interest expense											$ 81,000,000	87,000,000	85,000,000
AGC Trust Preferred Securities
Debt Instrument [Line Items]
Basis points											2.50%
AGM Trust Preferred Securities
Debt Instrument [Line Items]
Basis points											2.00%
AGUS (Issuer | AGMH
Debt Instrument [Line Items]
Debt instrument, fair value disclosure												154,000,000	$ 154,000,000
AGMH
Debt Instrument [Line Items]
Repayments of long-term debt					$ 200,000,000
AGM and AGC | AGM CPS securities
Debt Instrument [Line Items]
Number of custodial trusts | Trust											4
Maximum stock purchase obligation of each custodial trust											$ 200,000,000
Aggregate maximum stock purchase obligation of the custodial trusts											$ 50,000,000
AGC | AGM CPS securities
Debt Instrument [Line Items]
Rate basis for income distributions											one-month LIBOR
Assured Guaranty Municipal Corp
Debt Instrument [Line Items]
Principal											$ 1,726,000,000	1,728,000,000
Assured Guaranty Municipal Corp | AGM CPS securities
Debt Instrument [Line Items]
Rate basis for income distributions											one-month LIBOR
AGC
Debt Instrument [Line Items]
Loss on extinguishment of debt											$ 175,000,000
Loss on extinguishment of debt, net of tax											138,000,000
Acceleration of unamortized fair value adjustments											156,000,000
Junior Subordinated Debt | AGMH
Debt Instrument [Line Items]
Principal									$ 300,000,000		146,000,000	146,000,000
Effective interest rate of debt (as a percent)									6.40%
Interest rate, added to base rate (as a percent)									2.215%
Number of times interest payment may be deferred									1
Number of consecutive periods for which interest payments may be deferred | rISK									1
Period for which interest payment may be deferred (in years)									10 years
Number of times repayment date may be extended | extension									4
Repayment date extension measurement period									5 years
Notes Payable, Other Payables | Assured Guaranty Municipal Corp
Debt Instrument [Line Items]
Principal											$ 0	2,000,000
7% Senior Notes | Senior Notes | AGC
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
Net proceeds from issuance of debt										$ 197,000,000
Effective interest rate of debt (as a percent)											6.40%
5% Senior Notes
Debt Instrument [Line Items]
Payment for debt extinguishment											$ 19,000,000
5% Senior Notes | Senior Notes | AGC
Debt Instrument [Line Items]
Interest rate of debt (as a percent)							5.00%				5.00%
Principal			$ 500,000,000				$ 500,000,000				$ 330,000,000	330,000,000
Net proceeds from issuance of debt							$ 495,000,000
Repayments of long-term debt			170,000,000
3.15% Senior Notes | Senior Notes | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)						3.15%
3.15% Senior Notes | Senior Notes | AGC
Debt Instrument [Line Items]
Interest rate of debt (as a percent)											3.15%
Principal						$ 500,000,000					$ 500,000,000	500,000,000
Net proceeds from issuance of debt						$ 494,000,000
Redemption price percentage						100.00%
3.6% Senior Notes | Senior Notes | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)				3.60%
Repayments of long-term debt			400,000,000
3.6% Senior Notes | Senior Notes | AGC
Debt Instrument [Line Items]
Interest rate of debt (as a percent)											3.60%
Principal				$ 400,000,000							$ 400,000,000	$ 400,000,000
Net proceeds from issuance of debt				$ 395,000,000
Redemption price percentage				100.00%
Enhanced Junior Subordinated Debentures | Junior Subordinated Debt | AGMH
Debt Instrument [Line Items]
Period prior to final repayment date before which debt cannot be repaid, redeemed, repurchased or defeased (in years)									20 years
Enhanced Junior Subordinated Debentures | Junior Subordinated Debt | AGC
Debt Instrument [Line Items]
Principal								$ 150,000,000
Interest rate, added to base rate (as a percent)								2.38%
Number of times interest payment may be deferred								1
Number of consecutive periods for which interest payments may be deferred | period								1
Period for which interest payment may be deferred (in years)								10 years
6.875% QUIBS | Corporate securities | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)											6.875%
Repayments of long-term debt					100,000,000
6.25% Notes | Notes Payable, Other Payables | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)															6.25%
Principal					230,000,000
Repayments of long-term debt			130,000,000		$ 100,000,000
5.6% Notes | Corporate securities | AGMH
Debt Instrument [Line Items]
Repayments of long-term debt			$ 100,000,000
5.6% Notes | Notes Payable, Other Payables | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)														5.60%
Short Term Loan Facility | 6 Months | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 150,000,000
Maximum borrowing duration		6 months
Short Term Loan Facility | One Month | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 550,000,000
Proceeds from issuance of warehouse financing debt	$ 400,000,000
Short Term Loan Facility | One Month | Letter of Credit | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Interest rate, added to base rate (as a percent)		1.10%
Short Term Loan Facility | Thirty Days | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing duration		30 days