Lines of Credit and Financing Arrangements (Details Textual 1) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Nov. 13, 2014	Nov. 30, 2013	Nov. 12, 2014
Line of Credit Facility [Line Items]
Maximum securitization as percentage of net pool balance	100.00%
Program fee	0.60%
Average floating commercial paper rate	0.79%	0.78%
Unused fee	101.00%
Fixed rate of agreement	0.30%
Unused fee charged on incremental available amounts	0.05%
Minimum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount			$ 180,000,000	$ 160,000,000
Maximum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount			220,000,000	220,000,000
Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	950,000,000
Outstanding borrowings	482,000,000
Letters of credit	27,200,000
Remaining borrowing capacity	440,800,000
Maximum increase in borrowings under Domestic Revolving Credit Facility	350,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000				650,000,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	150,000,000
Subfacility for Swingline Loans [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	65,000,000
Term Loan [Member] | Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	300,000,000
Quarterly principal payment	7,500,000