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Financial Instruments and Fair Value Measurements - Impact of Interest Rate Derivative Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Amount of unrealized income (loss), net of tax, recognized in other comprehensive (loss) income	$ (36.7)	$ (13.3)
Amount of unrealized income (loss), net of tax, recognized in other comprehensive (loss) income			$ 6.5
Floorplan interest expense, net
Derivative [Line Items]
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations	(7.9)	(0.4)
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations			(4.7)
Other interest expense, net
Derivative [Line Items]
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations	$ (2.9)	$ 0.1
Amount of income (loss) reclassified from other comprehensive (loss) income into statements of operations			$ (0.5)

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Amount, after tax and before reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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