Debt (Schedule Of Letters Of Credit) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	$ 215,000,000
Letters of credit, Used	52,400,000
Letters of credit, Available	162,600,000
Letter of Credit [Member] | Bi-lateral Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	25,000,000	$ 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	150,000,000
Letters of credit, Limit	200,000,000	$ 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] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	40,000,000
Letters of credit, Used	35,300,000
Letters of credit, Available	$ 4,700,000