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Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Inventory [Line Items] |  |
Inventory | $ 3,771.4 | $ 3,650.5
New Vehicle [Member] |  |
Inventory [Line Items] |  |
Inventory | 3,040.9 | 2,874.8
Used Vehicle [Member] |  |
Inventory [Line Items] |  |
Inventory | 494.4 | 553.8
Parts and Service [Member] |  |
Inventory [Line Items] |  |
Inventory | $ 236.1 | $ 221.9

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