Segment Information (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues and segment income by reportable segment
Revenue	$ 4,904.4	$ 4,370.5	$ 9,375.5	$ 8,385.7
Segment income	143.7	122.7	259.6	225.0
Intersegment Elimination
Revenues and segment income by reportable segment
Revenue	(0.3)	(1.6)	(0.6)	(2.3)
Retail Automotive | Operating segments
Revenues and segment income by reportable segment
Revenue	4,538.6	4,256.5	8,713.6	8,175.7
Segment income	120.5	107.7	223.6	201.6
Retail Commercial Truck Dealership | Operating segments
Revenues and segment income by reportable segment
Revenue	241.9		434.6
Segment income	10.4	0.8	17.8	1.4
Other | Operating segments
Revenues and segment income by reportable segment
Revenue	124.2	115.6	227.9	212.3
Segment income	$ 12.8	$ 14.2	$ 18.2	$ 22.0