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Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2022 USD ($) Contract | Dec. 31, 2021 USD ($) Contract | Sep. 30, 2022 USD ($) | Mar. 31, 2021 USD ($) | Jun. 30, 2020 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |
Contracts outstanding | Contract | 13,382 | 12,350 |  |  |
Remaining weighted average contract period (in years) | 10 years 9 months 18 days | 10 years 9 months 18 days |  |  |
Principal | $ 99,996.9 | $ 89,196.5 | $ 42.5 | $ 805.5 | $ 36.9
Interest | 48,880.6 | 41,486.5 |  |  |
Total debt service outstanding | 148,877.5 | 130,683.0 |  |  |
Gross unearned insurance premiums (in millions) | $ 298.3 | $ 266.3 |  |  |

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