Income Taxes (Deferred Tax Inventory) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets related to:
U.S. federal and state net operating and capital loss carryforwards	$ 73.0	$ 104.3
Non-U.S. net operating loss carryforwards	33.9	34.0
Compensation	20.4	26.5
Investment basis difference	4.9	5.6
Other items	4.9	8.5
Total gross deferred income tax assets	137.1	178.9
Less: valuation allowances	109.6	146.2
Total net deferred income tax assets	27.5	32.7
Deferred income tax liabilities related to:
Other items	2.1	2.7
Total deferred income tax liabilities	26.2	32.7
Net deferred tax asset	1.3	0.0
Members Surplus Contributions
Deferred income tax liabilities related to:
Deferred tax liabilities, members surplus contributions	$ 24.1	$ 30.0