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Goodwill and Intangible Assets, Net (Intangible Assets) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived			$ 509.0	$ 566.5
Franchise rights impairment			57.5	9.6	$ 8.1
Nonrecurring [Member] | Franchise Rights [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights impairment	$ 0.0	$ 57.5		$ 9.6	$ 8.1
AN Reportable Segment, Domestic [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived			136.6
AN Reportable Segment, Import [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived			105.8
AN Reportable Segment, Premium Luxury [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived			$ 266.6

X

- Definition

Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16373-109275

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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- Definition

Carrying amount (original costs adjusted for previously recognized amortization and impairment) as of the balance sheet date for the rights acquired through a franchise arrangement having an indefinite period of benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
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+ References

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