Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	$ 1,255.7	$ 1,095.7
Other comprehensive income (loss) before reclassifications:
Pre-tax	(69.2)	(1.9)
Tax effect	9.7	1.3
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	(0.2)	0.1
Net current period other comprehensive income (loss)	(59.0)	(1.0)
BALANCE	1,174.6	1,127.7
Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.6	(0.3)
Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.1	(0.1)
Accumulated other comprehensive income (loss)
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(147.0)	(137.8)
Amounts reclassified from accumulated other comprehensive income (loss):
Net current period other comprehensive income (loss)	(59.0)	(1.0)
BALANCE	(206.0)	(138.7)
Accumulated income (loss) on foreign currency translation
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(142.9)	(146.7)
Other comprehensive income (loss) before reclassifications:
Pre-tax	(27.9)	3.6
Tax effect	0.0	0.0
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	0.0	0.0
Net current period other comprehensive income (loss)	(27.9)	3.6
BALANCE	(170.8)	(143.1)
Accumulated income (loss) on foreign currency translation | Floorplan interest expense (pre-tax)
Amounts 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)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.0	0.0
Accumulated income (loss) on interest rate swaps
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(4.1)	8.9
Other comprehensive income (loss) before reclassifications:
Pre-tax	(41.3)	(5.6)
Tax effect	9.7	1.3
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes	(0.2)	0.1
Net current period other comprehensive income (loss)	(31.1)	(4.6)
BALANCE	(35.2)	4.4
Accumulated income (loss) on interest rate swaps | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax	0.6	(0.3)
Accumulated income (loss) on interest rate swaps | Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax	$ 0.1	$ (0.1)