Debt (Senior Secured Credit Facility) (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Debt Instrument [Line Items]
Line of credit facility, letters of credit issued	$ 130.7	$ 128.4	$ 130.7
Credit Facility [Member]
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	$ 90.5	$ 88.2	$ 90.5
Line of credit facility, unused facility fee (percentage)	0.25%	0.35%
Line of credit facility, collateral, description			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.
Credit Facility [Member] | 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	153.0	$ 128.0	153.0
Line of credit facility, remaining borrowing capacity	349.1	554.9	349.1
Line of credit facility, remaining borrowing capacity available in either Canadian dollars or Mexican pesos	$ 146.6	$ 91.9	$ 146.6
Credit Facility [Member] | Revolving Loans [Member] | Weighted Average [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	4.19%	4.23%	4.19%
Credit Facility [Member] | 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			$ 5.0
Line of credit facility, interest rate (percentage)	4.00%	4.27%	4.00%
Credit Facility [Member] | Letters of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, capacity available for letters of credit	$ 349.1	$ 554.9	$ 349.1
Credit Facility [Member] | Letters of Credit [Member] | Performance Standby [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	0.625%	0.875%	0.625%
Credit Facility [Member] | Letters of Credit [Member] | Commercial and/or Financial Standby [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	1.50%	1.75%	1.50%