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Employee Benefit Plans - Narrative (Details) - USD ($) | 12 Months Ended
--- | ---
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 |  |

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- Definition 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. + References No definition available. + Details
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