Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Employee Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
Employee Benefit Plans - Narrative (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Employee benefit plans [Line Items]
Recognized contribution expense	$ 18,000,000	$ 16,000,000	$ 20,000,000
Sound Point Agreement \| Disposal Group, Held-for-Sale, Not Discontinued Operations
Employee benefit plans [Line Items]
Postretirement plan benefit obligation	$ 3,000,000	$ 8,000,000
U.S.
Employee benefit plans [Line Items]
Number of years of service to become fully vested	1 year
401 (k) Plan \| U.S.
Employee benefit plans [Line Items]
Percentage by which employer contribution matches up to 6% of participant's compensation	100.00%
Maximum percentage of participant's compensation eligible for employer contribution match	7.00%	7.00%	7.00%
Core contribution made by the company as a percentage of participant's compensation	7.00%	7.00%	7.00%
Nonqualified Supplemental Executive Retirement Plan \| U.S.
Employee benefit plans [Line Items]
Percentage by which employer contribution matches up to 6% of participant's compensation	100.00%
Maximum percentage of participant's compensation eligible for employer contribution match	6.00%
Core contribution made by the company as a percentage of participant's compensation	6.00%
Restricted Stock Units (RSUs)
Employee benefit plans [Line Items]
Unrecognized compensation expense	$ 14,000,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1 year 7 months 6 days
Total fair value of awards delivered	$ 16,000,000	$ 18,000,000	$ 12,000,000
Granted (in dollars per share)	$ 84.59	$ 61.26	$ 56.46
Restricted Stock Units (RSUs) \| Minimum
Employee benefit plans [Line Items]
Vesting period of awards (in years)	3 years
Performance Restricted Stock Units
Employee benefit plans [Line Items]
Vesting period of awards (in years)	3 years
Unrecognized compensation expense	$ 18,000,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1 year 10 months 24 days
Total fair value of awards delivered	$ 17,000,000	$ 11,000,000	$ 8,000,000
Granted (in dollars per share)	$ 94.56	$ 71.34	$ 62.89
Number of shares issued per right (in shares)	2
Performance Restricted Stock Units, Tied to Relative TSR
Employee benefit plans [Line Items]
Granted (in dollars per share)	$ 60.06
Number of shares issued per right (in shares)	2.5
Restricted Stock Awards
Employee benefit plans [Line Items]
Unrecognized compensation expense	$ 500,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	3 months 18 days
Granted (in dollars per share)	$ 77.54	$ 52.26	$ 59.47
Total fair value of awards vested	$ 2,000,000.0	$ 2,200,000	$ 2,300,000
Assured Guaranty Ltd 2024 Long-term Incentive Plan
Employee benefit plans [Line Items]
Maximum number of common shares that may be delivered (in shares)	1,750,000
Assured Guaranty Ltd 2024 Long-term Incentive Plan \| Stock Options
Employee benefit plans [Line Items]
Number of common shares available for grant (in shares)	1,731,773
Employee Stock Purchase Plan \| Employee Stock
Employee benefit plans [Line Items]
Number of common shares available for grant (in shares)	334,490
Value of shares that can be purchased as a percentage of participant's compensation	10.00%
Value of shares that can be purchased	$ 25,000
Purchase price of shares as a percentage of the fair market value of the stock	85.00%
Capital shares reserved for future issuance (in shares)	1,200,000