ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Increase (Decrease) in AOCI
BALANCE	$ 1,449.6	$ 1,255.7
Other comprehensive income (loss) before reclassifications:
Pre-tax	34.9	(69.2)
Tax effect	(9.4)	9.7
Amount reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	(0.7)	(0.2)
Net current period other comprehensive income (loss)	27.9	(59.0)
BALANCE	1,576.6	1,174.6
Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	2.2	0.6
Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.9	0.1
Accumulated other comprehensive income (loss)
Increase (Decrease) in AOCI
BALANCE	(184.0)	(147.0)
Amount reclassified from accumulated other comprehensive income (loss):
Net current period other comprehensive income (loss)	27.9	(59.0)
BALANCE	(156.2)	(206.0)
Accumulated income (loss) on foreign currency translation
Increase (Decrease) in AOCI
BALANCE	(151.6)	(142.9)
Other comprehensive income (loss) before reclassifications:
Pre-tax	(2.3)	(27.9)
Tax effect	0.0	0.0
Amount reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	0.0	0.0
Net current period other comprehensive income (loss)	(2.3)	(27.9)
BALANCE	(153.9)	(170.8)
Accumulated income (loss) on foreign currency translation \| Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.0	0.0
Accumulated income (loss) on foreign currency translation \| Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.0	0.0
Accumulated income (loss) on interest rate swaps
Increase (Decrease) in AOCI
BALANCE	(32.5)	(4.1)
Other comprehensive income (loss) before reclassifications:
Pre-tax	37.2	(41.3)
Tax effect	(9.4)	9.7
Amount reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	(0.7)	(0.2)
Net current period other comprehensive income (loss)	30.2	(31.1)
BALANCE	(2.3)	(35.2)
Accumulated income (loss) on interest rate swaps \| Floorplan interest expense (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	2.2	0.6
Accumulated income (loss) on interest rate swaps \| Other interest expense, net (pre-tax)
Amount reclassified from accumulated other comprehensive income (loss):
Pre-tax	$ 0.9	$ 0.1

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