Debt (Schedule Of Letters Of Credit) (Details)	Dec. 31, 2017 USD ($)
Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	$ 204,600,000
Letters of credit, Used	53,300,000
Letters of credit, Available	151,300,000
Letter of Credit [Member] | Bi-lateral Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	25,000,000
Letters of credit, Used	17,100,000
Letters of credit, Available	7,900,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letter of credit maximum sublimit	150,000,000
Letters of credit, Limit	200,000,000
Revolving Credit Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Available	150,000,000
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Used	40,000,000
Accounts Receivable Securitization Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	29,600,000
Letters of credit, Used	36,200,000
Letters of credit, Available	$ (6,600,000)