Intangible Assets (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	$ 1,322.8	$ 1,270.4	$ 1,139.0
Goodwill, Additions	83.7	165.4
Goodwill, Foreign currency translation	31.3	34.0
Impairment of intangible assets	0.0	0.0	$ 0.0
Retail Automotive
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	1,095.3	1,053.6
Goodwill, Additions	63.9	53.7
Goodwill, Foreign currency translation	23.5	24.7
Retail Commercial Truck Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	147.5	127.7
Goodwill, Additions	19.8	127.7
Other
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	$ 80.0	$ 89.1