Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended			12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Sep. 30, 2022	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018	Jan. 01, 2025	Jun. 30, 2020	Jan. 31, 2020	Dec. 31, 2012
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of risk premium ceded	60.00%		60.00%			60.00%
Insurance-linked securities, term			12 years				12 years	12 years
Insurance-linked securities, callable term			7 years				5 years	5 years
HG Re
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of par value of policy reinsured	15.00%		15.00%			15.00%
Trust balance	$ 288.6	$ 250.2	$ 288.6			$ 288.6	$ 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%			15.00%
Percent over a target trust balance						102.00%
Supplement trust target	$ 603.0		$ 603.0			$ 603.0
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Principal	99,996.9	89,196.5	99,996.9	$ 42.5	$ 805.5	99,996.9	89,196.5			$ 36.9
HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Collateral held in supplement trust	856.9	852.0	856.9			856.9	852.0
Cash and investments included in collateral trust	503.3	481.7	503.3			503.3	481.7
Interest receivable	157.9	157.6	157.9			157.9	157.6
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Surplus notes	340.0	364.6	340.0			340.0	364.6
Interest receivable	13.6	5.7	13.6			13.6	5.7
Accrued interest on surplus notes	157.9	157.6	157.9			157.9	157.6
Supplemental Trust | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	24.6	23.6
Accrued interest on surplus notes	1.0	0.4	1.0			1.0	0.4
Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	36.0	33.8
Accrued interest on surplus notes	10.4	9.8	$ 10.4			10.4	$ 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%	90.00%
Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Insurance linked securities	150.0	150.0	$ 150.0			150.0	$ 150.0	$ 100.0
Aggregate loss limit on contracts	110.0	135.0	110.0			110.0	135.0	165.0
Reimbursement guarantee under contracts	150.0	150.0	$ 150.0			$ 150.0	150.0	100.0
Percentage of financial guaranty policies covered			33.00%			32.00%
Percentage of quota share reinsurance agreement				100.00%	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						27.00%
Maximum | BAM | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts											$ 125.0
Maximum | Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts	276.7	301.7	$ 276.7			$ 276.7	301.7	$ 276.1
Series A BAM Surplus Note | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Trust balance	$ 568.3	$ 601.8	$ 568.3			$ 568.3	$ 601.8
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)	7.70%		7.70%			7.70%