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Investments and Cash - Narrative (Details) | 12 Months Ended
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Dec. 31, 2022 USD ($) manager Security | Dec. 31, 2021 USD ($) Security | Dec. 31, 2020 USD ($)
Schedule of Cost-method Investments [Line Items] |  |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Fair value gains (losses) on trading securities |  |
Number of investment portfolio managers | manager | 3 |  |
Accrued investment income | $ 71,000,000 | $ 69,000,000 |
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | Security | 567 | 23 |
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more | $ 329,000,000 | $ 6,000,000 |
Assets held-in-trust | 222,000,000 | 243,000,000 |
Non-income producing investments | 0 | 0 |
Credit loss expense | 21,000,000 | 7,000,000 | $ 17,000,000
Purchased with credit deterioration, amount at purchase price | 22,000,000 |  |
Securities purchased with credit deterioration, amount at par value | 31,000,000 |  |
Allowance for credit loss at acquisition date | 2,000,000 |  |
Discount attributable to other factors | 7,000,000 |  |
PCI Securities |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Credit loss expense | 21,000,000 | 6,000,000 | 16,000,000
Assured Guaranty Subsidiaries |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Assets held-in-trust | 1,169,000,000 | 1,231,000,000 |
Future Equity Investments |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Purchase commitment, remaining minimum amount committed | 78,000,000 |  |
AssuredIM Funds | Equity in Earnings (Losses) of Investees | Assured Guaranty Asset Strategies LLC |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Fair value of investment | 569,000,000 | 543,000,000 |
AssuredIM Funds | Equity in Earnings (Losses) of Investees | Assured Guaranty Subsidiaries |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Long-term purchase commitment, amount | 755,000,000 |  |
AssuredIM Funds | Future Equity Investments | Assured Guaranty Subsidiaries |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Authorized amount to invest | 750,000,000 |  |
Investments, including distributed gains, authorized amount to invest | 810,000,000 |  |
AssuredIM Funds | Invested Capital | Assured Guaranty Subsidiaries |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Long-term purchase commitment, amount | 536,000,000 |  |
AssuredIM Funds | Unfunded Commitment | Assured Guaranty Subsidiaries |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Long-term purchase commitment, amount | 219,000,000 |  |
Equity Securities |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Cash dividends from subsidiaries | $ 10,000,000 | $ 15,000,000 | $ 10,000,000

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