Lines of Credit and Financing Arrangements (Details Textual) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	May 31, 2010
Lines of Credit and Financing Arrangements (Textual) [Abstract]
Maximum securitization, amount	$ 150.0
Maximum securitization as percentage of net pool balance	100.00%
Program fee	0.60%
Average floating commercial paper rate	0.86%	0.91%
Basis of unused fee	Unused fee is based on 102% of the maximum available amount less the beneficial interest sold and calculated at a 0.30% fixed rate throughout the term of the agreement
Unused fee	102.00%
Fixed rate of agreement	0.30%
Domestic revolving credit facility [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility	650
Borrowings under Domestic Revolving Credit Facility	297.5
Committed standby letters of credit	58.5
Available for future borrowings	294.0
Indebtedness to Adjusted EBITDA Ratio	3.5:1.0
Cash Flow to Net Interest Expense ratio	3.0:1.0
Maximum increase in borrowings under Domestic Revolving Credit Facility	100
Extended maturity date	Oct. 31, 2016
Senior Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes	200.0	200.0	200.0
Fixed interest rate for senior unsecured notes	4.90%
Maturity date of senior unsecured notes	May 15, 2017
Default long term debt description of violation or event of default of revolving credit facility	The indenture governing the notes contains covenants limit our ability and the ability of the subsidiary guarantors to: create or incur certain liens; enter into certain sale and leaseback transactions; enter into certain mergers, consolidations and transfers of substantially all of our assets; and transfer certain properties.Indenture also contains a cross default provision which is triggered if we default on other debt of at least $75 million in principal which is then accelerated, and such acceleration is not rescinded within 30 days of the notice date
Minimum principal amount accelerated	$ 75
Notice Date	30 days