Municipal Bond Guarantee - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Gross earned premiums	$ 6.2	$ 5.2	$ 17.2	$ 13.7
HG/BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Direct written premiums	14.4	10.2	45.5	30.6
Assumed written premiums	0.0	10.6	0.1	10.6
Gross written premiums		20.8	45.6	41.2
Direct premiums earned	5.3	4.4	14.5	11.9
Assumed premiums earned	0.9	0.8	2.7	1.8
Gross earned premiums	$ 6.2	$ 5.2	$ 17.2	$ 13.7