Contracts Accounted for as Insurance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Weighted average risk-free rates for U.S. dollar denominated financial guaranty insurance obligations	1.02%	0.60%
Net Par Outstanding	$ 236,392	$ 234,153
Gross	367,770	366,692
Increase (decrease) in net par due to commutations		336
Commutation gains (losses)	0	38	$ 1
Gross Exposure	1,605	1,484
Puerto Rico
Guarantor Obligations [Line Items]
Net Par Outstanding	3,572	3,725
Gross	$ 5,322	5,674
Net par exposures reassumed		$ 118
Variable Rate Demand Obligation
Guarantor Obligations [Line Items]
Bonds held by bank, minimum installment payment period	5 years
Assured Guaranty Municipal Corp
Guarantor Obligations [Line Items]
Maximum termination payment	$ 21
AGM and AGC | Variable Rate Demand Obligation
Guarantor Obligations [Line Items]
Net Par Outstanding	1,700
AGM and AGC | Variable Rate Demand Obligation | Internal Credit, B Minus Rating
Guarantor Obligations [Line Items]
Net Par Outstanding	25
Assumed Business
Guarantor Obligations [Line Items]
Insured financial obligations insured contractual payments outstanding, amount represented	$ 16,300
Insured financial obligations insured contractual payments outstanding, percentage represented	4.40%
AGC
Guarantor Obligations [Line Items]
Amounts could be required to pay if third party exercised right to recapture business	$ 233
AG Re
Guarantor Obligations [Line Items]
Amounts could be required to pay if third party exercised right to recapture business	33
Ceded Business
Guarantor Obligations [Line Items]
Insured financial obligations insured contractual payments outstanding, amount represented	$ 410
Insured financial obligations insured contractual payments outstanding, percentage represented	0.10%
Gross Insured Specialty and Reinsurance Business
Guarantor Obligations [Line Items]
Insured financial obligations insured contractual payments outstanding, amount represented	$ 534
ARGO | Uncollateralized
Guarantor Obligations [Line Items]
Guaranty liabilities	$ 14
Minimum
Guarantor Obligations [Line Items]
Risk free discount rate	0.00%	0.00%
Minimum | Variable Rate Demand Obligation
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	2.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	90 days
Maximum
Guarantor Obligations [Line Items]
Risk free discount rate	1.98%	1.72%
Maximum | Variable Rate Demand Obligation
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	3.00%
Bank bond capped rate (as a percent)	25.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	180 days
Premiums Receivable | Foreign Currency Concentration Risk | Premiums Receivable
Guarantor Obligations [Line Items]
Percentage of installment premiums denominated in currencies other than the U.S. dollar	78.00%	80.00%