Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Jun. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Written premiums:
Direct					$ 24.1
Assumed					14.0
Gross written premiums					38.1
Earned premiums:
Direct					15.8
Assumed					8.5
Gross earned premiums					24.3
HG Global
Written premiums:
Direct	$ 0.0	$ 0.0		$ 0.0	0.0
Assumed	15.9	14.0		41.8	34.5
Gross written premiums	15.9	14.0	$ 20.5	41.8	34.5
Earned premiums:
Direct	0.0	0.0		0.0	0.0
Assumed	7.5	7.5		22.8	21.5
Gross earned premiums	$ 7.5	$ 7.5	$ 14.0	$ 22.8	21.5
BAM
Written premiums:
Direct					24.1
Assumed					0.0
Gross written premiums					24.1
Earned premiums:
Direct					15.8
Assumed					1.0
Gross earned premiums					16.8
Eliminations
Written premiums:
Direct					0.0
Assumed					(20.5)
Gross written premiums					(20.5)
Earned premiums:
Direct					0.0
Assumed					(14.0)
Gross earned premiums					$ (14.0)