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Municipal Bond Guarantee Insurance (Tables) | 12 Months Ended
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Dec. 31, 2019
Insurance [Abstract] |
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table Text Block] | The following table presents a schedule of BAM’s future premium revenues as of December 31, 2019:
Millions |  | December 31, 2019
January 1, 2020 - March 31, 2020 |  | $ | 4.8 |
April 1, 2020 - June 30, 2020 |  | 4.8 |
July 1, 2020 - September 30, 2020 |  | 4.6 |
October 1, 2020 - December 31, 2020 |  | 4.5 |
|  | 18.7 |
2021 |  | 17.3 |
2022 |  | 16.3 |
2023 |  | 15.2 |
2024 |  | 14.2 |
2025 and thereafter |  | 116.7 |
Total gross unearned insurance premiums |  | $ | 198.4 |
Schedule of Insured Obligations | The following table presents a schedule of BAM’s insured obligations as of December 31, 2019 and 2018:
|  | December 31, 2019 |  | December 31, 2018
Contracts outstanding |  | 8,987 |  |  | 7,525 |
Remaining weighted average contract period (in years) |  | 10.7 |  |  | 10.7 |
Contractual debt service outstanding (in millions): |  |  |  |
Principal |  | $ | 62,250.5 |  |  | $ | 52,201.6 |
Interest and capital appreciation |  | 31,799.7 |  |  | 26,560.3 |
Total debt service outstanding |  | $ | 94,050.2 |  |  | $ | 78,761.9 |
Gross unearned insurance premiums |  | $ | 198.4 |  |  | $ | 176.0 |
Schedule of Net Written Premiums | The following table presents a schedule of net written premiums and net earned premiums included in White Mountains’s HG Global/BAM segment for the years ended December 31, 2019, 2018 and 2017:
Millions |  | December 31, 2019 |  | December 31, 2018 |  | December 31, 2017
Written premiums: |  |  |  |  |  |
Direct |  | $ | 28.1 |  |  | $ | 44.8 |  |  | $ | 63.2 |
Assumed |  | 10.6 |  |  | 8.1 |  |  | — |
Gross written premiums |  | $ | 38.7 |  |  | $ | 52.9 |  |  | $ | 63.2 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 13.6 |  |  | $ | 13.6 |  |  | $ | 9.4 |
Assumed |  | 2.7 |  |  | .3 |  |  | — |
Gross earned premiums |  | $ | 16.3 |  |  | $ | 13.9 |  |  | $ | 9.4 |

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- Definition Tabular disclosure of financial guarantee insurance contracts in which premiums are received over the contract period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290 + Details
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- Definition [Table Text Block] for Schedule of Municipal Guarantee Insured Obligations [Table] + References No definition available. + Details
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- Definition Schedule of Net Written Premiums [Table Text Block] + References No definition available. + Details
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