Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 31, 2020	Mar. 31, 2021	Jun. 30, 2018	Dec. 31, 2021	Jan. 01, 2025	Dec. 31, 2022	Jun. 30, 2020	Sep. 30, 2019	Dec. 31, 2012
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of risk premium ceded	60.00%					60.00%
Insurance-linked securities, term				12 years	12 years
Insurance-linked securities, callable term				5 years	5 years
Cash and investments included in collateral trust	$ 481.7					$ 481.7
HG Re
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of par value of policy reinsured	15.00%					15.00%
Trust balance	$ 250.2	$ 222.8				$ 250.2
HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Surplus notes											$ 503.0
Percentage of par value of policy reinsured	15.00%					15.00%
Percent over a target trust balance						102.00%
Supplement trust target	$ 603.0					$ 603.0
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Principal	89,196.5	75,287.7		$ 800.0		89,196.5				$ 1,100.0
Additional municipal bond guarantee									$ 36.9
HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Collateral held in supplement trust	852.0	827.1				852.0
Cash and investments included in collateral trust	481.7	434.5				481.7
Interest receivable	157.6	155.7				157.6
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Surplus notes	364.6	388.2				364.6
Interest receivable	5.7	4.4				5.7
Accrued interest on surplus notes	157.6	155.7				157.6
Supplemental Trust | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	23.6	21.5	$ 47.9
Accrued interest on surplus notes	0.4	0.2	0.9			0.4
Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	33.8	30.1	65.0
Accrued interest on surplus notes	9.8	8.4	16.2			$ 9.8
BAM | Fidus Re Ltd.
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Losses above retention, percentage of liability				90.00%	90.00%
Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Insurance linked securities				$ 150.0	$ 100.0
Aggregate loss limit on contracts				135.0	165.0
Reimbursement guarantee under contracts				$ 150.0	100.0
Percentage of financial guaranty policies covered						38.00%
Percentage of quota share reinsurance agreement				100.00%
Fidus Re Ltd. | BAM | 2018 Covered Portfolio
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of financial guaranty policies covered						33.00%
Maximum | BAM | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts			$ 75.0
Maximum | Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts				$ 301.7	$ 276.1
Series A BAM Surplus Note | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Trust balance	$ 601.8	$ 604.3				$ 601.8
Fixed interest rate | Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Interest rate	8.00%					8.00%
Fixed interest rate | Surplus Note | BAM | Forecast
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Interest rate							8.00%
U.S. treasury rate plus | Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Basis spread on variable rate						3.00%
Effective yield (as a percent)	3.20%					3.20%
U.S. treasury rate plus | Surplus Note | BAM | Forecast
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Effective yield (as a percent)								3.20%