Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	$ 1,174.6	$ 1,127.7	$ 1,255.7	$ 1,095.7
Other comprehensive income (loss) before reclassifications:
Pre-tax			(80.2)	(18.4)
Tax effect			11.2	4.3
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes			(0.8)	0.2
Net current period other comprehensive income (loss)	(7.3)	(13.8)	(66.4)	(14.8)
BALANCE	1,215.9	1,164.1	1,215.9	1,164.1
Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax			2.7	(0.6)
Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax			0.8	(0.2)
Accumulated other comprehensive income (loss)
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(206.0)	(138.7)	(147.0)	(137.8)
Amounts reclassified from accumulated other comprehensive income (loss):
Net current period other comprehensive income (loss)	(7.3)	(13.8)	(66.4)	(14.8)
BALANCE	(213.3)	(152.5)	(213.3)	(152.5)
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			(30.4)
Tax effect			0.0
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes			0.0
Net current period other comprehensive income (loss)			(30.4)	(0.4)
BALANCE	(173.2)	(147.1)	(173.2)	(147.1)
Accumulated income (loss) on foreign currency translation | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax			0.0
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
Accumulated income (loss) on interest rate swaps
Increase (Decrease) in AOCI [Roll Forward]
BALANCE			(4.1)
Other comprehensive income (loss) before reclassifications:
Pre-tax			(49.8)
Tax effect			11.2
Amounts reclassified from accumulated other comprehensive income (loss):
Provision (benefit) for income taxes			(0.8)
Net current period other comprehensive income (loss)			(36.0)	(14.3)
BALANCE	$ (40.1)	$ (5.4)	(40.1)	$ (5.4)
Accumulated income (loss) on interest rate swaps | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax			2.7
Accumulated income (loss) on interest rate swaps | Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss):
Pre-tax			$ 0.8