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Inventories (Components of Inventories, net) (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Inventory [Line Items] |  |
Total inventories | $ 2,441.0 | $ 2,365.3
New vehicles |  |
Inventory [Line Items] |  |
Total inventories | 1,784.9 | 1,700.1
Used vehicles |  |
Inventory [Line Items] |  |
Total inventories | 568.6 | 576.8
Parts and accessories |  |
Inventory [Line Items] |  |
Total inventories | $ 87.5 | $ 88.4

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