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Municipal Bond Guarantee - Narrative (Details) $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 31, 2020 USD ($)	Apr. 30, 2018 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 yr	Jun. 30, 2020 USD ($) Contract	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Contract	Dec. 31, 2018 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2024	Dec. 31, 2020	Sep. 30, 2019 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2012 USD ($)
Guarantor Obligations [Line Items]
Ownership interest (as a percent)			50.00%			53.80%		50.00%
Percent change in discounted future cash flows						10.00%
Repayments of debt						$ 1.1	$ 21.7
Interest paid						$ 6.7	$ 7.3
HG Global
Guarantor Obligations [Line Items]
Partners capital contribution										$ 594.5
Surplus notes															$ 503.0
Cash and Fixed Income Securities															100.0
Percent over a target trust balance						102.00%
Supplement Trust Target						$ 603.0
HG Global \| Preferred Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)						96.90%		96.60%
HG Global \| Common Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)			88.40%			88.40%		89.60%
BAM
Guarantor Obligations [Line Items]
Percentage of risk premium ceded			60.00%
Number of years of change in interest rate									3
Year of U.S. Treasury rate \| yr					1
Contracts outstanding \| Contract						9,992		8,987
Remaining weighted average contract period outstanding (in years)						10 years 7 months 6 days		10 years 8 months 12 days
Municipal bond outstanding principal						$ 67,591.5		$ 62,250.5					$ 1,100.0
Municipal bond outstanding interest						33,775.8		31,799.7
Municipal bond debt service outstanding						101,367.3		94,050.2
April 1, 2020 - December 31, 2020						10.2
2021						19.6
2022						18.5
2023						17.3
2024						16.2
2025						15.0
2026 and thereafter						121.8
Total gross unearned insurance premiums						218.6		198.4
HG Global
Guarantor Obligations [Line Items]
Collateral held in supplement trust						811.8		786.7
Interest receivable						$ 155.0		162.7
HG Re
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured						15.00%
BAM
Guarantor Obligations [Line Items]
Surplus notes						$ 409.7		457.6
Interest receivable						$ 4.7		$ 7.5
BAM Management
Guarantor Obligations [Line Items]
Partners capital contribution										$ 14.5
Supplemental Trust [Member] \| BAM
Guarantor Obligations [Line Items]
Repayments of Unsecured Debt			$ 47.9
Accrued Interest Payment on Surplus Notes			0.9
Surplus Note \| BAM
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)								5.70%
Repayments of Unsecured Debt			65.0
Accrued Interest Payment on Surplus Notes			$ 16.2
Combination One \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate \| yr					5
US Treasury Rate \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Basis spread on variable rate						3.00%
Fixed interest rate \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)				8.00%					8.00%
First Quarter, year two \| BAM
Guarantor Obligations [Line Items]
2021						$ 5.0
Second Quarter, year two \| BAM
Guarantor Obligations [Line Items]
2021						4.9
Third Quarter, year two \| BAM
Guarantor Obligations [Line Items]
2021						4.9
Fourth Quarter, year two \| BAM
Guarantor Obligations [Line Items]
2021						$ 4.8
Series A BAM Surplus Note \| HG Global
Guarantor Obligations [Line Items]
Surplus notes														$ 203.0	203.0
Series B BAM Surplus Note \| HG Global
Guarantor Obligations [Line Items]
Surplus notes															$ 300.0
BAM \| Fidus Re Ltd.
Guarantor Obligations [Line Items]
Losses above retention, percentage of liability		90.00%
BAM \| HG Global
Guarantor Obligations [Line Items]
Term of Agreement	10 years
Fidus Re Ltd. \| BAM
Guarantor Obligations [Line Items]
Secured Debt		$ 100.0
Municipal bond outstanding principal				$ 2,200.0					$ 2,200.0
Collateralized financial guarantee, term		12 years
Collateral financial guarantee, callable term			5 years
Aggregate losses on ceded business		$ 165.0
Premium receivable, Premium expected to be collected		100.0
Percentage of Quota Share Reinsurance Agreement				100.00%
Maximum \| BAM \| HG Global
Guarantor Obligations [Line Items]
Aggregate losses on ceded business	$ 75.0
Maximum \| Fidus Re Ltd. \| BAM
Guarantor Obligations [Line Items]
Aggregate losses on ceded business		$ 276.1
Scenario, Forecast \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)												4.60%
Scenario, Forecast \| Fixed interest rate \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Derivative, fixed interest rate (as a percent)											8.00%