Lines of Credit and Financing Arrangements (Asset Securitization Program, Textuals) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Nov. 13, 2017	Dec. 31, 2016	Jul. 05, 2016
Line of Credit Facility [Line Items]
Maximum securitization, amount				$ 325,000,000
Maximum securitization as percentage of net pool balance	100.00%
Program fee (as a percent)	0.70%
Average floating commercial paper rate (as a percent)	2.60%		1.66%
Unused fee (as a percent)	101.00%
Fixed rate of agreement (as a percent)	0.35%
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
Maximum [Member]
Line of Credit Facility [Line Items]
Amount Available Under Asset Securitization		$ 380,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Amount Available Under Asset Securitization		$ 225,000,000		$ 200,000,000