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Employee Benefit Plans - Narrative (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Employee benefit plans [Line Items] |  |  |
Recognized contribution expense | $ 20,000,000 | $ 20,000,000 | $ 20,000,000
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 | $ 21,000,000 |  |
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years) | 1 year 9 months 18 days |  |
Total fair value of awards delivered | $ 12,000,000 | $ 12,000,000 | $ 11,000,000
Granted (in dollars per share) | $ 56.46 | $ 44.08 | $ 41.31
Restricted Stock Units (RSUs) | Minimum |  |  |
Employee benefit plans [Line Items] |  |  |
Vesting period of awards (in years) | 3 years |  |
Restricted Stock Units (RSUs) | Maximum |  |  |
Employee benefit plans [Line Items] |  |  |
Vesting period of awards (in years) | 4 years |  |
Performance Restricted Stock Units |  |  |
Employee benefit plans [Line Items] |  |  |
Unrecognized compensation expense | $ 15,000,000 |  |
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years) | 1 year 8 months 12 days |  |
Total fair value of awards delivered | $ 8,000,000 | $ 9,000,000 | $ 8,000,000
Granted (in dollars per share) | $ 62.89 | $ 41.34 |
Number of shares issued per right (in shares) | 2 |  |
Vesting period of awards (in years) | 3 years |  |
Performance Restricted Stock Units, Tied to Relative TSR |  |  |
Employee benefit plans [Line Items] |  |  |
Granted (in dollars per share) | $ 62.89 | 52.04 | $ 41.03
Number of shares issued per right (in shares) | 2.5 |  |
Restricted Stock Awards |  |  |
Employee benefit plans [Line Items] |  |  |
Unrecognized compensation expense | $ 700,000 |  |
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years) | 3 months 18 days |  |
Granted (in dollars per share) | $ 59.47 | $ 51.34 | $ 28.12
Total fair value of awards vested | $ 2,300,000 | $ 1,900,000 | $ 2,300,000
Assured Guaranty Ltd. 2004 Long-Term Incentive Plan |  |  |
Employee benefit plans [Line Items] |  |  |
Maximum number of common shares that may be delivered (in shares) | 18,670,000 |  |
Assured Guaranty Ltd. 2004 Long-Term Incentive Plan | Stock Options |  |  |
Employee benefit plans [Line Items] |  |  |
Number of common shares available for grant (in shares) | 8,059,991 |  |
Employee Stock Purchase Plan | Employee Stock |  |  |
Employee benefit plans [Line Items] |  |  |
Number of common shares available for grant (in shares) | 65,042 |  |
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) | 850,000 |  |

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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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- Definition Represents the core contribution made by the employer to the plan for participating employees as a percentage of participant compensation, regardless of participant contribution. + References No definition available. + Details
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- Definition Represents the total fair value of equity-based awards delivered to a grantee during the period. + References No definition available. + Details
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- Definition The highest value of shares an employee can purchase under the plan per period. + References No definition available. + Details
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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(01) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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