Debt (Schedule of Letters of Credit Facilities) (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	$ 211,200,000
Letters of credit, Used	47,600,000
Letters of credit, Available	163,600,000
Letter of Credit [Member] | Bi-lateral Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	25,000,000.0	$ 25,000,000.0
Letters of credit, Used	11,400,000
Letters of credit, Available	13,600,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letter of credit maximum sublimit	150,000,000.0	150,000,000.0
Letters of credit, Limit	200,000,000.0	$ 200,000,000.0
Revolving Credit Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Available	150,000,000.0
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Used	36,200,000
Accounts Receivable Securitization Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	36,200,000
Letters of credit, Used	$ 36,200,000