Segment Information (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) item	Jun. 30, 2019 USD ($)
Segment Reporting Information
Number of reportable segments \| item			4
Number of operating segments \| item			6
Revenues and segment income by reportable segment
Revenues	$ 3,651.1	$ 5,755.8	$ 8,660.2	$ 11,320.2
Segment income	61.2	159.9	$ 132.7	293.7
Operating segments
Segment Reporting Information
Number of reportable segments \| item			1
Retail Automotive Dealership
Revenues and segment income by reportable segment
Revenues	3,153.5	5,196.3	$ 7,570.1	10,287.5
Retail Automotive Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	3,153.5	5,196.3	7,570.1	10,287.5
Segment income	11.8	98.1	53.1	183.0
Retail Commercial Truck Dealership
Revenues and segment income by reportable segment
Revenues	399.2	426.8	890.6	759.1
Retail Commercial Truck Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	399.2	426.8	890.6	759.1
Segment income	14.6	18.9	28.3	34.8
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	98.4	132.7	199.5	273.6
Segment income	4.9	4.9	7.8	12.1
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Segment income	$ 29.9	$ 38.0	$ 43.5	$ 63.8

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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