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Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended
	Jan. 31, 2021	Dec. 31, 2020	Jan. 31, 2020	Mar. 31, 2021	Jun. 30, 2018	Sep. 30, 2021	Dec. 31, 2021	Jun. 30, 2020	Dec. 31, 2012	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		$ 376.4				$ 710.4
HG Global
Guarantor Obligations [Line Items]
Collateral held in supplement trust		827.1				844.8
Collateral trusts, investments and cash		434.5				449.7
BAM
Guarantor Obligations [Line Items]
Surplus notes		388.2				388.2
Interest receivable		4.4				$ 6.9
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]
Surplus notes										$ 203.0
Assets Held-in-trust		604.3				$ 603.8
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		222.8				$ 241.0
BAM
Guarantor Obligations [Line Items]
Additional municipal bond guarantee								$ 36.9
Principal	$ 800.0	75,287.7				83,829.0
BAM | HG Global
Guarantor Obligations [Line Items]
Interest receivable		155.7				164.8
BAM | Surplus Note
Guarantor Obligations [Line Items]
Repayments of unsecured debt		30.1	65.0
Accrued interest payment on surplus notes		8.4	16.2
BAM | Surplus Note | HG Global
Guarantor Obligations [Line Items]
Debt		388.2				$ 388.2
BAM | Supplemental Trust
Guarantor Obligations [Line Items]
Repayments of unsecured debt		21.5	47.9
Accrued interest payment on surplus notes		$ 0.2	$ 0.9
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							3.10%
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						36.00%
BAM | Fidus Re Ltd. | 2021 Covered Portfolio
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered						40.00%
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%

X

- Definition

The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of premium receivables under financial guarantee insurance contracts.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Amount of expected guaranteed benefits in excess of the projected account balances for minimum guaranteed benefit contracts, as of the balance sheet date.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

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Additional Municipal Bond Guarantee

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Collateral Held in Supplement Trust

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Collateral Trusts, Investments And Cash

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Insurance Linked Securities, Callable Term

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Losses Above Retention, Percentage of Liability

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Municipal bond outstanding principal

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Percentage Of Financial Guaranty Policies Covered

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Percentage of par value of policy reinsured.

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Percentage of Risk Premium Ceded

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Percent over a target trust balance

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Supplement Trust Target

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