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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
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-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 225
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-Section S99
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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 of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Segment Information (Details) $ in Millions	3 Months Ended		12 Months Ended
Segment Information (Details) $ in Millions	Mar. 31, 2018 USD ($) item	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information
Number of reportable segments \| item	4
Revenues and segment income by reportable segment
Revenues	$ 5,746.9	$ 5,081.1
Adjusted segment income	$ 144.3	124.7
Retail Automotive Dealership
Segment Reporting Information
Number of reportable segments \| item	1
Number of operating segments \| item	6
Revenues and segment income by reportable segment
Revenues	$ 5,296.0	4,756.4	$ 19,800.0
Retail Automotive Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	5,296.0	4,756.4
Adjusted segment income	106.6	104.8
Retail Commercial Truck Dealership
Revenues and segment income by reportable segment
Revenues	292.4	211.7
Retail Commercial Truck Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	292.4	211.7
Adjusted segment income	12.1	6.5
Commercial Vehicle Distribution and Other
Revenues and segment income by reportable segment
Revenues	158.5	113.0
Commercial Vehicle Distribution and Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	158.5	113.0
Adjusted segment income	9.6	0.9
Non-Automotive Investments \| Operating segments
Revenues and segment income by reportable segment
Adjusted segment income	$ 16.0	$ 12.5