Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Dec. 31, 2021	Jan. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Jun. 30, 2018	Dec. 31, 2022	Jan. 31, 2020	Jul. 31, 2012
Guarantor Obligations [Line Items]
Percentage of risk premium ceded			60.00%
Insurance-linked securities, term				12 years	12 years
Insurance-linked securities, callable term				5 years	5 years
Debt	$ 693.0		$ 690.9
HG Global
Guarantor Obligations [Line Items]
Collateral held in supplement trust	852.0		836.3
Collateral trusts, investments and cash	481.7		466.0
BAM
Guarantor Obligations [Line Items]
Surplus notes	364.6		364.6
Interest receivable	5.7		5.7
HG Global
Guarantor Obligations [Line Items]
Surplus notes			$ 503.0					$ 503.0
Percentage of par value of policy reinsured			15.00%
Percent over a target trust balance			102.00%
Supplement trust target			$ 603.0
HG Global | Series A BAM Surplus Note
Guarantor Obligations [Line Items]
Assets Held-in-trust	601.8		$ 591.5
HG Global | BAM | Maximum
Guarantor Obligations [Line Items]
Aggregate losses on ceded business							$ 75.0
HG Re
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured			15.00%
Assets Held-in-trust	250.2		$ 244.8
BAM
Guarantor Obligations [Line Items]
Principal	89,196.5	$ 805.5	91,609.8
BAM | HG Global
Guarantor Obligations [Line Items]
Interest receivable	157.6		160.6
BAM | Surplus Note
Guarantor Obligations [Line Items]
Repayments of unsecured debt	33.8
Accrued interest payment on surplus notes	9.8
BAM | Surplus Note | HG Global
Guarantor Obligations [Line Items]
Debt	364.6		$ 364.6
BAM | Supplemental Trust
Guarantor Obligations [Line Items]
Repayments of unsecured debt	23.6
Accrued interest payment on surplus notes	$ 0.4
BAM | US Treasury (UST) Interest Rate | Surplus Note
Guarantor Obligations [Line Items]
Basis spread on variable rate			3.00%
BAM | Fixed interest rate | Surplus Note
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)			8.00%
BAM | Forecast | US Treasury (UST) Interest Rate | Surplus Note
Guarantor Obligations [Line Items]
Effective percentage						3.20%
BAM | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Secured debt				$ 150.0	$ 100.0
Aggregate losses on ceded business				135.0	165.0
Premium receivable, Premium expected to be collected				150.0	100.0
Percentage of quota share reinsurance agreement		100.00%
BAM | Fidus Re Ltd. | 2018 Covered Portfolio
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered			32.00%
BAM | Fidus Re Ltd. | 2021 Covered Portfolio
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered			36.00%
BAM | Fidus Re Ltd. | Maximum
Guarantor Obligations [Line Items]
Aggregate losses on ceded business				$ 301.7	$ 276.1
Fidus Re Ltd. | BAM
Guarantor Obligations [Line Items]
Losses above retention, percentage of liability				90.00%	90.00%