Income Taxes (Effective Rate Reconciliation) (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
Income Tax Contingency [Line Items]
U.S. statutory rate (as a percent)	21.00%	35.00%									35.00%
Tax expense (benefit) at the U.S. statutory rate											$ (2.7)	$ 51.6	$ (45.2)
Differences in taxes resulting from:
Tax rate changes											(44.3)	(3.9)	(0.5)
Change in valuation allowance											42.6	6.9	(21.8)
Non-U.S. earnings, net of foreign taxes											21.5	(19.2)	58.5
Officer compensation											(4.1)	0.0	0.0
Member surplus contributions											(3.0)	(2.3)	(1.5)
Withholding tax											(2.0)	(0.2)	(0.5)
Tax exempt interest and dividends											0.5	0.1	0.0
Tax reserve adjustments											(0.3)	0.0	0.0
Other, net											(0.4)	(0.1)	(1.7)
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)
Pre-tax (loss) income from continuing operations			$ 5.2	$ 8.4	$ (2.2)	$ (3.6)	$ (74.5)	$ (13.8)	$ (25.7)	$ (33.3)	7.8	(147.3)	129.2
Tax Payments and Receipts
Net income tax payments to (receipts from) national governments, total											2.0	0.3	0.7
Non-US
Differences in taxes resulting from:
Pre-tax (loss) income from continuing operations											$ 71.3	$ (66.3)	$ 149.5