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Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Earned premiums: |  |
Gross earned premiums | $ 111.0 | $ 5.4
HG/BAM |  |
Written premiums: |  |
Direct | 8.0 | 9.7
Assumed | 4.5 | 0.0
Gross written premiums | 12.5 | 9.7
Earned premiums: |  |
Direct | 5.3 | 4.5
Assumed | 1.1 | 0.9
Gross earned premiums | $ 6.4 | $ 5.4

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