Intangible Assets - Changes in Goodwill by Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	$ 1,752.0	$ 1,660.5
Goodwill, Additions	146.6	144.1
Goodwill, Disposals	(3.9)	(13.8)
Goodwill, Foreign currency translation	16.3	(38.8)
Goodwill, Ending balance	1,911.0	1,752.0
Retail Automotive Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	1,511.9	1,412.1
Goodwill, Additions	0.9	143.2
Goodwill, Disposals	(3.9)	(13.8)
Goodwill, Foreign currency translation	15.9	(29.6)
Goodwill, Ending balance	1,524.8	1,511.9
Retail Commercial Truck Dealership
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	162.6	163.0
Goodwill, Additions	145.6	0.9
Goodwill, Foreign currency translation	0.8	(1.3)
Goodwill, Ending balance	309.0	162.6
Other
Summary of the changes in the carrying amount of goodwill by reportable segment
Goodwill, Beginning balance	77.5	85.4
Goodwill, Additions	0.1
Goodwill, Foreign currency translation	(0.4)	(7.9)
Goodwill, Ending balance	77.2	77.5
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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