Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Inventory	$ 3,677.0	$ 3,305.8
New Vehicle [Member]
Inventory [Line Items]
Inventory	2,840.9	2,490.8
Used Vehicle [Member]
Inventory [Line Items]
Inventory	600.2	570.0
Parts and Service [Member]
Inventory [Line Items]
Inventory	$ 235.9	$ 245.0

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118951113&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116846819&loc=d3e3927-108312

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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Balance Type:	debit
Period Type:	instant