Goodwill And Intangible Assets, Net (Details) $ in Millions		3 Months Ended
		Mar. 31, 2020 USD ($) store		Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)		Dec. 31, 2019 USD ($)
Goodwill [Line Items]
Goodwill	[1]	$ 1,183.6	[2]		$ 1,183.6	[2]	$ 1,501.9
Franchise rights - indefinite-lived					509.0		566.5
Other intangibles					21.2		23.4
Other intangible assets, gross					530.2		589.9
Less: accumulated amortization					(7.9)		(8.3)
Other intangible assets, net					522.3		581.6
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	1,501.9
Acquisitions, dispositions, and other adjustments, net	[3]	0.0
Impairment		(318.3)		$ 0.0
Goodwill, ending balance	[1],[2]	$ 1,183.6
Accumulated impairment loss					1,470.0		1,470.0
Franchise rights impairment, number of stores | store		8
Franchise rights impairment		$ 57.5		$ 0.0
Reporting Unit, Domestic [Member]
Goodwill [Line Items]
Goodwill	[1]	227.3	[2]		227.3	[2]	227.3
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	227.3
Acquisitions, dispositions, and other adjustments, net	[3]	0.0
Impairment		0.0
Goodwill, ending balance	[1],[2]	227.3
Accumulated impairment loss					140.0		140.0
Reporting Unit, Import [Member]
Goodwill [Line Items]
Goodwill	[1]	498.8	[2]		498.8	[2]	498.9
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	498.9
Acquisitions, dispositions, and other adjustments, net	[3]	(0.1)
Impairment		0.0
Goodwill, ending balance	[1],[2]	498.8
Reporting Unit, Premium Luxury [Member]
Goodwill [Line Items]
Goodwill	[1]	457.5	[2]		457.5	[2]	714.9
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	714.9
Acquisitions, dispositions, and other adjustments, net	[3]	0.0
Impairment		(257.4)
Goodwill, ending balance	[1],[2]	457.5
Accumulated impairment loss					257.4
Reporting Unit, Collision Centers [Member]
Goodwill [Line Items]
Goodwill	[1]	0.0	[2]		0.0	[2]	41.7
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	41.7
Acquisitions, dispositions, and other adjustments, net	[3]	(0.1)
Impairment		(41.6)
Goodwill, ending balance	[1],[2]	0.0
Accumulated impairment loss					41.6
Reporting Unit, Parts Centers [Member]
Goodwill [Line Items]
Goodwill	[1]	0.0	[2]		0.0	[2]	$ 19.1
Goodwill [Roll Forward]
Goodwill, beginning balance	[1]	19.1
Acquisitions, dispositions, and other adjustments, net	[3]	0.2
Impairment		(19.3)
Goodwill, ending balance	[1],[2]	0.0
Accumulated impairment loss					$ 19.3
Franchise Rights [Member]
Goodwill [Roll Forward]
Franchise rights impairment		$ 57.5

[1] Net of accumulated impairment losses of $1.47 billion associated with our single reporting unit (prior to September 30, 2008, our reporting unit structure was comprised of a single reporting unit) and $140.0 million associated with our Domestic reporting unit, both of which were recorded during the year ended December 31, 2008.

[2] Net of accumulated impairment losses of $257.4 million associated with our Premium Luxury reporting unit, $41.6 million associated with our Collision Centers reporting unit, and $19.3 million associated with our Parts Centers reporting unit, each of which were recorded during the three months ended March 31, 2020.

[3] Includes amounts reclassified to held for sale and related adjustments, which are presented in Other Current Assets in our Consolidated Balance Sheet as of period end.