INVENTORIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of Inventory [Line Items]
Total inventories	$ 985.0	$ 1,067.6
Lower of cost or market inventory reserves	6.1	6.1
Held-for-sale
Components of Inventory [Line Items]
Total inventories	67.7
New vehicles
Components of Inventory [Line Items]
Total inventories	802.6	867.2
Reduction of new vehicle inventory cost by automobile manufacturer incentives	9.6	10.1
Reduction to new vehicle cost of sales by automobile manufacturer incentives	45.7	42.4	$ 40.1
Used vehicles
Components of Inventory [Line Items]
Total inventories	140.1	158.9
Parts and accessories
Components of Inventory [Line Items]
Total inventories	$ 42.3	$ 41.5