Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended			12 Months Ended
	Mar. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018	Jan. 01, 2025	Dec. 31, 2023	Mar. 31, 2021	Jun. 30, 2018	Jul. 31, 2012
Guarantor Obligations [Line Items]
Percentage of risk premium ceded	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 Global
Guarantor Obligations [Line Items]
Collateral held in supplement trust	$ 880,700,000	$ 880,700,000	$ 856,900,000		$ 856,900,000
Collateral trusts, investments and cash	520,600,000	520,600,000	503,300,000		503,300,000
BAM
Guarantor Obligations [Line Items]
Surplus notes	340,000,000	340,000,000	340,000,000		340,000,000
Interest receivable	20,100,000	20,100,000	13,600,000		13,600,000
Series A BAM Surplus Note | BAM
Guarantor Obligations [Line Items]
Interest receivable	164,500,000	164,500,000	157,900,000		157,900,000
HG Global
Guarantor Obligations [Line Items]
Surplus notes	$ 503,000,000	$ 503,000,000										$ 503,000,000
Percentage of par value of policy reinsured	15.00%	15.00%
Percent over a target trust balance		102.00%
Supplement trust target	$ 603,000,000	$ 603,000,000
HG Global | Series A BAM Surplus Note
Guarantor Obligations [Line Items]
Assets Held-in-trust	579,900,000	$ 579,900,000	568,300,000		568,300,000
HG Global | BAM | Maximum
Guarantor Obligations [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Life	$ 125,000,000
HG Re
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured	15.00%	15.00%
Assets Held-in-trust	$ 300,800,000	$ 300,800,000	288,600,000		288,600,000
BAM | Surplus Note
Guarantor Obligations [Line Items]
Repayments of unsecured debt		$ 0	36,000,000	$ 0
Accrued interest payment on surplus notes			10,400,000		10,400,000
BAM | Supplemental Trust
Guarantor Obligations [Line Items]
Repayments of unsecured debt			24,600,000
Accrued interest payment on surplus notes			1,000,000		1,000,000
BAM | US Treasury (UST) Interest Rate | Surplus Note
Guarantor Obligations [Line Items]
Basis spread on variable rate		3.00%
BAM | Forecast | US Treasury (UST) Interest Rate | Surplus Note
Guarantor Obligations [Line Items]
Effective percentage									7.70%
BAM | Forecast | Fixed interest rate | Surplus Note
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)								8.00%
BAM | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Secured debt			$ 150,000,000		150,000,000					$ 150,000,000	$ 100,000,000
Reinsurance, Limit on Total Reimbursement					150,000,000	$ 150,000,000	$ 100,000,000
Percentage of financial guaranty policies covered		32.00%
BAM | Fidus Re Ltd. | 2018 Covered Portfolio
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered		26.00%
BAM | Fidus Re Ltd. | 2021 Covered Portfolio
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered		31.00%
BAM | Fidus Re Ltd. | Maximum
Guarantor Obligations [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Life					276,700,000	301,700,000	276,100,000
BAM | Fidus Re Ltd. | Minimum
Guarantor Obligations [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Life					$ 110,000,000	$ 135,000,000	$ 165,000,000
Fidus Re Ltd. | BAM
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured					90.00%	90.00%	90.00%