Revenue Earning Equipment (Details Textuals) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Revenue Earning Equipment (Textuals) [Abstract]
Cost	$ 9,473,236,000	$ 9,473,236,000	$ 9,269,518,000
Accumulated Depreciation	3,485,433,000	3,485,433,000	3,514,910,000
Effect of change in estimated residual values of revenue earning equipment on pre tax earnings	7,400,000	14,900,000
Assets Held under Capital Leases [Member]
Revenue Earning Equipment (Textuals) [Abstract]
Cost	54,900,000	54,900,000	56,200,000
Accumulated Depreciation	$ 18,300,000	$ 18,300,000	$ 16,500,000