Intangible Assets - Changes in Goodwill by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	$ 1,291.3	$ 1,323.2	$ 1,270.8
Goodwill, Additions	24.9	83.7
Goodwill, Disposals	1.7
Goodwill, Foreign currency translation	55.1	31.3
Impairment of intangible assets	0.0	0.0	$ 0.0
Retail Automotive Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	1,050.3	1,095.7
Goodwill, Additions	9.8	63.9
Goodwill, Disposals	0.2
Goodwill, Foreign currency translation	55.0	23.5
Retail Commercial Truck Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	162.0	147.5
Goodwill, Additions	15.1	19.8
Goodwill, Foreign currency translation	0.6
Other
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	79.0	80.0
Non-Automotive Investments
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill	$ 0.0	$ 0.0