Reconciliation of Federal Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Taxes computed at the federal rate		$ (30.3)	$ (256.9)	$ (167.3)
Goodwill impairment		36.6	0.0	0.0
State and local income taxes, net of federal tax benefit		0.0	(26.8)	(20.6)
Valuation allowance		(14.5)	171.5	74.5
Repatriation of foreign earnings		14.2	2.1	13.4
Change in federal tax rate and law change	$ (4.1)	(4.1)	0.0	0.0
Foreign earnings taxed at different rate		(7.2)	(5.3)	(11.2)
Adjustment to prior years’ taxes		(5.2)	3.4	(5.4)
Foreign exchange differences		2.6	0.0	0.0
Withholding taxes		2.2	0.0	0.0
Other		(1.1)	5.1	4.5
Income tax benefit		$ (6.8)	$ (106.9)	$ (112.1)