Taxation (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense (Benefit) per 2017 Tax Act		$ (130,700,000)
Tax benefit due to change in tax rate		130,700,000
Transition tax on foreign earnings		$ 0
Statutory tax rate		35.00%	35.00%	35.00%
Deferred Tax Assets, Operating Loss Carryforwards		$ 413,300,000	$ 243,800,000
Unremitted Foreign Earnings		988,000,000	897,200,000
Deferred Tax Liabilities, Undistributed Foreign Earnings		1,400,000	900,000
Unrecognized Tax Benefits		19,600,000	10,500,000	$ 9,600,000	$ 6,000,000
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		3,100,000	0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		16,500,000	9,500,000
Income tax provision		(268,200,000)	(338,300,000)	(398,000,000)
Expiring In Next Five Fiscal Years [Member]
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration		35,200,000
Expiring In After Five Fiscal Years [Member]
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration		15,200,000
Indefinite Life [Member]
Deferred Tax Assets, Operating Loss Carryforwards		362,900,000
Change during the period [Member]
Deferred Tax Assets, Increase (Decrease) in Operating Loss Carryforward		169,500,000
Operating Loss Carryforwards resulting from acquisitions [Member]
Deferred Tax Assets, Increase (Decrease) in Operating Loss Carryforward		160,100,000
Operating Loss Carryforwards resulting from FX [Domain]
Deferred Tax Assets, Increase (Decrease) in Operating Loss Carryforward		(23,100,000)
General Business Tax Credit Carryforward [Member]
Deferred Tax Assets, Increase (Decrease) in Operating Loss Carryforward		$ (15,800,000)
Forfeiture of losses resulting from liquidations or mergers [Member]
Deferred Tax Assets, Increase (Decrease) in Operating Loss Carryforward	$ 30,000,000
Canada
Dividends Withholding Tax Rate		5.00%
ILLINOIS
Unrecognized Tax Benefits, Period Increase (Decrease)		$ 11,000,000
Related to accrued interest and penalties [Member]
Income Tax Examination, Penalties and Interest Accrued		2,900,000	1,700,000	1,200,000
Income tax provision		(1,200,000)	$ (500,000)	$ (900,000)
Minimum [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound		0
Maximum [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound		$ 10,000,000