Segment Information (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) item	Jun. 30, 2015 USD ($)
Segment Reporting Information
Number of reportable Segments \| item			3
Number of geographic operating segments \| item			4
Revenues and segment income by reportable segment
Revenues	$ 5,254.1	$ 4,920.6	$ 10,078.7	$ 9,403.5
Segment income	143.5	143.5	263.1	259.1
Intersegment Elimination
Revenues and segment income by reportable segment
Revenues	(0.7)	(0.3)	(1.7)	(0.6)
Retail Automotive \| Operating segments
Revenues and segment income by reportable segment
Revenues	4,836.8	4,554.9	9,349.7	8,741.7
Segment income	123.1	120.3	233.5	223.1
Retail Commercial Truck Dealership \| Operating segments
Revenues and segment income by reportable segment
Revenues	309.5	241.9	516.2	434.6
Segment income	7.6	10.4	13.4	17.8
Other \| Operating segments
Revenues and segment income by reportable segment
Revenues	108.5	124.1	214.5	227.8
Segment income	$ 12.8	$ 12.8	$ 16.2	$ 18.2

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51673353&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 10
-Article 5

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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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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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