Inventory and Vehicle Floorplan Payable (Components of Inventory) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Inventory [Line Items]
Inventory	$ 1,847.9	$ 2,598.5
New Vehicle [Member]
Inventory [Line Items]
Inventory	515.1	1,761.9
Used Vehicle [Member]
Inventory [Line Items]
Inventory	1,109.3	648.4
Parts and Service [Member]
Inventory [Line Items]
Inventory	$ 223.5	$ 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
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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