Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Inventory [Line Items]
Inventory	$ 3,226.9	$ 2,899.0
New Vehicle [Member]
Inventory [Line Items]
Inventory	2,543.3	2,294.3
Used Vehicle [Member]
Inventory [Line Items]
Inventory	511.6	437.6
Parts and Service [Member]
Inventory [Line Items]
Inventory	$ 172.0	$ 167.1

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=51655945&loc=d3e3927-108312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

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