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Municipal Bond Guarantee - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 USD ($) Contract | Dec. 31, 2019 USD ($) Contract | Sep. 30, 2019 USD ($)
Guarantor Obligations [Line Items] |  |  |
Contracts outstanding | Contract | 10,495 | 8,987 |
Remaining weighted average contract period outstanding (in years) | 10 years 8 months 12 days | 10 years 8 months 12 days |
Municipal bond outstanding principal | $ 70,954.1 | $ 62,250.5 | $ 1,100.0
Municipal bond outstanding interest | 34,842.8 | 31,799.7 |
Municipal bond debt service outstanding | 105,796.9 | 94,050.2 |
Total gross unearned insurance premiums | $ 226.9 | $ 198.4 |

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