Municipal Bond Guarantee Reinsurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Written premiums:
Direct		$ 24.1	$ 58.6	$ 63.8
Assumed		31.9	0.0	1.3
Gross written premiums		56.0	58.6	65.1
Earned premiums:
Direct		15.8	28.7	28.6
Assumed Premiums Earned		15.9	2.5	4.7
Gross earned premiums		31.7	31.2	33.3
HG Global
Written premiums:
Direct		0.0	0.0	0.0
Assumed		52.4	50.1	55.9
Gross written premiums		52.4	50.1	55.9
Earned premiums:
Direct		0.0	0.0	0.0
Assumed Premiums Earned		28.9	26.0	27.5
Gross earned premiums		28.9	26.0	27.5
BAM
Written premiums:
Direct		24.1	58.6	63.8
Assumed		0.0	0.0	1.3
Gross written premiums		24.1	58.6	65.1
Earned premiums:
Direct		15.8	28.7	28.6
Assumed Premiums Earned		1.0	2.5	4.7
Gross earned premiums		16.8	31.2	33.3
Ceded Premiums Written	$ (20.5)		(50.1)	(55.9)
Ceded to Other Companies	$ (14.0)		(26.0)	(27.5)
Eliminations
Written premiums:
Direct		0.0	0.0	0.0
Assumed		(20.5)	(50.1)	(55.9)
Gross written premiums		(20.5)	(50.1)	(55.9)
Earned premiums:
Direct		0.0	0.0	0.0
Assumed Premiums Earned		(14.0)	(26.0)	(27.5)
Gross earned premiums		$ (14.0)	$ (26.0)	$ (27.5)