Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Earned premiums:
Net earned premiums	$ 262.8	$ 202.8
HG/BAM
Written premiums:
Direct	9.2	9.4
Assumed	0.0	0.0
Net written premiums	9.2	9.4
Earned premiums:
Direct	7.0	7.6
Assumed	0.7	0.8
Net earned premiums	$ 7.7	$ 8.4

Amount of earned premiums assumed from other entities.

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