Debt (Senior Secured Credit Facility) (Narrative) (Details) - Credit Facility [Member] - USD ($) $ in Millions			1 Months Ended	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2017	Mar. 31, 2018
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,500.0			$ 1,500.0
Line of credit facility, letters of credit issued	$ 131.7	$ 157.1	$ 157.1	$ 131.7
Line of credit facility, unused facility fee (percentage)	0.30%	0.25%
Line of credit facility, collateral				The Credit Facility is guaranteed by certain subsidiaries of the Company (the “Guarantor Subsidiaries”) and the obligations under the Credit Facility are secured by substantially all of the Company’s and the Guarantor Subsidiaries’ respective assets, subject to certain exceptions.
Revolving Loans [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,100.0			$ 1,100.0
Line of credit facility, amount of borrowings denominated in foreign currencies	112.0	$ 117.0	117.0	112.0
Line of credit facility, remaining borrowing capacity	514.5	565.2	565.2	514.5
Line of credit facility, remaining borrowing capacity available in either Canadian dollars or Mexican pesos	$ 187.7	$ 183.4	$ 183.4	$ 187.7
Revolving Loans [Member] | Weighted Average [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	3.98%	3.69%	3.69%	3.98%
Term Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 400.0			$ 400.0
Line of credit facility, term loan, frequency of payments				quarterly
Line of credit facility, term loan, amount of quarterly principal installment payments			$ 3.1	$ 5.0
Line of credit facility, interest rate (percentage)	3.50%	3.07%	3.07%	3.50%
Letters of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, capacity available for letters of credit	$ 514.5	$ 492.9	$ 492.9	$ 514.5
Letters of Credit [Member] | Performance Standby [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	0.75%	0.625%	0.625%	0.75%
Letters of Credit [Member] | Commercial and/or Financial Standby [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	1.625%	1.50%	1.50%	1.625%