Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Supplemental Cash Flow Information [Abstract]
Non-cash investing and financing activities primarily related to capital leases	$ 21.2	$ 2.0
Accrued purchases of property and equipment	15.2	13.8
Interest payments including interest on vehicle inventory financing	68.2	67.8
Income tax payments, net of income tax refunds	$ 161.0	$ 140.6