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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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Segment Information (Details) $ in Millions	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information
Number of reportable segments \| item			4
Number of operating segments \| item			6
Revenues and segment income by reportable segment
Revenues	$ 5,967.6	$ 5,658.6	$ 17,287.8	$ 17,345.8
Segment income	158.4	157.1	$ 452.1	477.6
Operating segments
Segment Reporting Information
Number of reportable segments \| item			1
Retail Automotive Dealership
Revenues and segment income by reportable segment
Revenues	5,155.4	5,148.5	$ 15,442.9	15,900.0	$ 20,800.0
Retail Automotive Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	5,155.4	5,148.5	15,442.9	15,900.0
Segment income	79.7	94.6	262.7	318.2
Retail Commercial Truck Dealership
Revenues and segment income by reportable segment
Revenues	692.3	385.3	1,451.4	1,016.5
Retail Commercial Truck Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	692.3	385.3	1,451.4	1,016.5
Segment income	30.7	19.1	65.5	47.2
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	119.9	124.8	393.5	429.3
Segment income	5.9	2.6	18.0	20.4
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Segment income	$ 42.1	$ 40.8	$ 105.9	$ 91.8