Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - HG Global/BAM - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Written premiums:
Direct	$ 16.5	$ 18.4	$ 37.3	$ 44.9
Assumed	0.0	1.3	0.0	1.3
Gross written premiums	16.5	19.7	37.3	46.2
Earned premiums:
Direct	7.4	6.5	21.4	22.0
Assumed	0.5	0.6	1.9	4.0
Gross earned premiums	$ 7.9	$ 7.1	$ 23.3	$ 26.0