Lines of Credit and Financing Arrangements (Domestic Credit Facility) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016	Jan. 23, 2019	Nov. 13, 2014
Line of Credit Facility [Line Items]
Proceeds from the facilities		$ 28,400,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity				$ 650,000,000
Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings	$ 408,000,000
Standby letters of credit	2,500,000
Line of credit, available for future borrowings	429,500,000
Maximum increase in credit facility	350,000,000
Domestic Credit Facility [Member] | Medium-term Notes [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount				$ 250,000,000
Outstanding borrowings	190,000,000
Quarterly principal repayments	7,500,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	100,000,000.0
Subfacility for Swingline Loans [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	65,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Minimum amount of principal or interest due on indebtedness or receivable securitization	$ 75,000,000.0
Subsequent Event [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity			$ 1,000,000,000.0
Subsequent Event [Member] | Domestic Credit Facility [Member] | Medium-term Notes [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 350,000,000.0