Intangible Assets - Changes in Goodwill by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	$ 1,660.5	$ 1,291.2
Goodwill, Additions	144.1	324.8
Goodwill, Disposals	(13.8)	(4.5)
Goodwill, Foreign currency translation	(38.8)	49.0
Goodwill, Ending balance	1,752.0	1,660.5
Retail Automotive Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	1,412.1	1,050.2
Goodwill, Additions	143.2	324.8
Goodwill, Disposals	(13.8)	(4.5)
Goodwill, Foreign currency translation	(29.6)	41.6
Goodwill, Ending balance	1,511.9	1,412.1
Retail Commercial Truck Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	163.0	162.0
Goodwill, Additions	0.9
Goodwill, Foreign currency translation	(1.3)	1.0
Goodwill, Ending balance	162.6	163.0
Other
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	85.4	79.0
Goodwill, Foreign currency translation	(7.9)	6.4
Goodwill, Ending balance	77.5	85.4
Non-Automotive Investments
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	0.0
Goodwill, Ending balance	$ 0.0	$ 0.0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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