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Long-Term Debt and Credit Facilities - Principal and Carrying Amounts of Debt (Details) - USD ($) | Dec. 31, 2022 | Dec. 31, 2021 | Sep. 27, 2021 | Aug. 20, 2021 | May 26, 2021 | Jun. 20, 2014 | Nov. 22, 2006 | May 18, 2004
--- | --- | --- | --- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Carrying Value | $ (1,675,000,000) | $ (1,673,000,000) |  |  |  |  |  |
Assured Guaranty Municipal Corp |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Principal | 1,726,000,000 | 1,728,000,000 |  |  |  |  |  |
Carrying Value | $ (1,675,000,000) | (1,673,000,000) |  |  |  |  |  |
Senior Notes | AGC | 7% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) | 700.00% |  |  |  |  |  |  | 700.00%
Principal | $ 200,000,000 | 200,000,000 |  |  |  |  |  | $ 200,000,000
Carrying Value | $ (198,000,000) | (197,000,000) |  |  |  |  |  |
Senior Notes | AGC | 5% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) | 5.00% |  |  |  |  | 5.00% |  |
Principal | $ 330,000,000 | 330,000,000 | $ 500,000,000 |  |  | $ 500,000,000 |  |
Carrying Value | $ (329,000,000) | (329,000,000) |  |  |  |  |  |
Senior Notes | AGC | 3.15% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) | 3.15% |  |  |  |  |  |  |
Principal | $ 500,000,000 | 500,000,000 |  |  | $ 500,000,000 |  |  |
Carrying Value | $ (495,000,000) | (495,000,000) |  |  |  |  |  |
Senior Notes | AGC | 3.6% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) | 3.60% |  |  |  |  |  |  |
Principal | $ 400,000,000 | 400,000,000 |  | $ 400,000,000 |  |  |  |
Carrying Value | (395,000,000) | (395,000,000) |  |  |  |  |  |
Senior Notes | AGMH | 3.15% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) |  |  |  |  | 3.15% |  |  |
Senior Notes | AGMH | 3.6% Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rate of debt (as a percent) |  |  |  | 3.60% |  |  |  |
Enhanced Junior Subordinated Debentures | AGC |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Principal | 150,000,000 | 150,000,000 |  |  |  |  |  |
Carrying Value | (150,000,000) | (150,000,000) |  |  |  |  |  |
Junior Subordinated Debentures | AGMH |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Principal | 146,000,000 | 146,000,000 |  |  |  |  | $ 300,000,000 |
Carrying Value | (108,000,000) | (105,000,000) |  |  |  |  |  |
Notes Payable, Other Payables | Assured Guaranty Municipal Corp |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Principal | 0 | 2,000,000 |  |  |  |  |  |
Carrying Value | $ 0 | $ (2,000,000) |  |  |  |  |  |

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