Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Inventory [Line Items]
Inventory	$ 2,254.6	$ 2,598.5
New Vehicle [Member]
Inventory [Line Items]
Inventory	1,363.6	1,761.9
Used Vehicle [Member]
Inventory [Line Items]
Inventory	698.8	648.4
Parts and Service [Member]
Inventory [Line Items]
Inventory	$ 192.2	$ 188.2

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=121566466&loc=d3e6676-107765

Reference 2: 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=120391452&loc=d3e13212-122682

Name:	us-gaap_InventoryNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant