Revenue Earning Equipment (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue Earning Equipment (Textual) [Abstract]
Cost	$ 9,269,518,000	$ 8,512,030,000
Accumulated Depreciation	3,514,910,000	3,462,359,000
Effect of change in estimated residual values of revenue earning equipment on pre tax earnings	18,000,000	5,000,000	14,000,000
Assets held under capital leases [Member]
Revenue Earning Equipment (Textual) [Abstract]
Cost	56,000,000	61,000,000
Accumulated Depreciation	$ 17,000,000	$ 14,000,000