Long-Term Debt and Credit Facilities - Narrative (Details)											12 Months Ended
	Sep. 25, 2023 USD ($)	Aug. 21, 2023 USD ($)	Aug. 16, 2023	Sep. 27, 2021 USD ($)	Aug. 20, 2021 USD ($)	May 26, 2021 USD ($)	Jun. 20, 2014 USD ($)	Dec. 20, 2006 USD ($) period	Nov. 22, 2006 USD ($) rISK extension	May 18, 2004 USD ($)	Dec. 31, 2023 USD ($) Trust	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 09, 2021 USD ($)
Debt Instrument [Line Items]
Principal											$ 1,746,000,000	$ 1,726,000,000
Net proceeds from issuance of debt											345,000,000	0	$ 889,000,000
Repayments of long-term debt											330,000,000	2,000,000	620,000,000
Loss on extinguishment of debt											0	0	175,000,000
Interest expense											90,000,000	81,000,000	87,000,000
AGUS (Issuer | AGMH
Debt Instrument [Line Items]
Debt instrument, fair value disclosure												154,000,000	154,000,000
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
AGM and AGC | AGM CPS securities
Debt Instrument [Line Items]
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]
Number of custodial trusts | Trust											4
Assured Guaranty Municipal Corp | AGM CPS securities
Debt Instrument [Line Items]
Number of custodial trusts | Trust											4
Junior Subordinated Debt | AGMH
Debt Instrument [Line Items]
Principal									$ 300,000,000		$ 146,000,000	146,000,000
Interest rate, added to base rate (as a percent)									2.33%
Effective interest rate of debt (as a percent)									6.40%
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 | AGMH
Debt Instrument [Line Items]
Principal														$ 430,000,000
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				$ 0	330,000,000
Net proceeds from issuance of debt							$ 495,000,000
Repayments of long-term debt	$ 330,000,000			$ 170,000,000
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%
Interest rate, added to base rate (as a percent)			0.30%
3.6% Senior Notes | Senior Notes | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)					3.60%
Senior Notes 6.125 Percent | Senior Notes | AGC
Debt Instrument [Line Items]
Interest rate of debt (as a percent)		6.125%									6.125%
Principal		$ 350,000,000									$ 350,000,000	0
Net proceeds from issuance of debt		$ 345,000,000
Redemption price percentage		100.00%
Interest rate, added to base rate (as a percent)			0.30%
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%
Interest rate, added to base rate (as a percent)			0.25%
3.15% Senior Notes | Senior Notes | AGMH
Debt Instrument [Line Items]
Interest rate of debt (as a percent)						3.15%
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%
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)								2.64%
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
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