Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Earned premiums:
Net earned premiums	$ 202.8	$ 111.0
HG/BAM
Written premiums:
Direct	9.4	8.0
Assumed	0.0	4.5
Net written premiums	9.4	12.5
Earned premiums:
Direct	7.6	5.3
Assumed	0.8	1.1
Net earned premiums	$ 8.4	$ 6.4

Amount of earned premiums assumed from other entities.

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