Income Taxes (Valuation Allowance) (Details) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Dec. 22, 2017	Dec. 21, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Valuation allowance			$ 109.6				$ 146.2				$ 109.6	$ 146.2
Change in valuation allowance											$ (42.6)	(6.9)	$ 21.8
U.S. statutory rate (as a percent)	21.00%	35.00%									35.00%
Income Tax Expense (Benefit)			(2.5)	$ (4.0)	$ (1.0)	$ (0.3)	(10.2)	$ (17.1)	$ (4.0)	$ (1.6)	$ (7.8)	(32.9)	$ 12.7
U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Valuation allowance			74.8				112.5				74.8	112.5
United Kingdom | Net operating losses in UK Subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance											0.7	0.1
Unites States
Valuation Allowance [Line Items]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense											43.1
Unites States | U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Change in valuation allowance											6.4
Non-US | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance												2.8
Israel | Net operating losses in Israel Subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance											3.0	3.4
Subsidiaries | Net operating losses in Israel Subsidiaries
Valuation Allowance [Line Items]
Valuation allowance			13.5				9.4				13.5	9.4
Subsidiaries | Luxembourg | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance			20.3				24.0				20.3	24.0
Subsidiaries | United Kingdom | Net operating losses in UK Subsidiaries
Valuation Allowance [Line Items]
Valuation allowance			$ 1.0				$ 0.3				1.0	0.3
Guilford Holdings, Inc. | Unites States
Valuation Allowance [Line Items]
Change in valuation allowance											(21.5)	17.1
U.S. statutory rate (as a percent)	21.00%	35.00%
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense											20.4
BAM
Valuation Allowance [Line Items]
Change in valuation allowance											(18.4)	3.6
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense											22.7
Income Tax Expense (Benefit)											(10.1)	(11.0)
Star & Shield Insurance Exchange
Valuation Allowance [Line Items]
Decrease in valuation allowance												$ (6.9)
Continuing Operations | Guilford Holdings, Inc. | Unites States
Valuation Allowance [Line Items]
Change in valuation allowance											$ (21.4)