Segment Information (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) item	Sep. 30, 2019 USD ($)
Segment Reporting Information
Number of reportable segments \| item			4
Number of operating segments \| item			6
Revenues and segment income by reportable segment
Revenues	$ 5,971.6	$ 5,967.6	$ 14,631.8	$ 17,287.8
Segment income	311.6	158.4	$ 444.3	452.1
Operating segments
Segment Reporting Information
Number of reportable segments \| item			1
Retail Automotive Dealership
Revenues and segment income by reportable segment
Revenues	5,258.0	5,155.4	$ 12,828.1	15,442.9
Retail Automotive Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	5,258.0	5,155.4	12,828.1	15,442.9
Segment income	215.4	79.7	268.5	262.7
Retail Commercial Truck Dealership
Revenues and segment income by reportable segment
Revenues	590.9	692.3	1,481.5	1,451.4
Retail Commercial Truck Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	590.9	692.3	1,481.5	1,451.4
Segment income	23.4	30.7	51.7	65.5
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	122.7	119.9	322.2	393.5
Segment income	8.3	5.9	16.1	18.0
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Segment income	$ 64.5	$ 42.1	$ 108.0	$ 105.9

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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