Goodwill and Intangible Assets, Net (Intangible Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	$ 566.5	$ 580.1
AN Reportable Segment, Domestic [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	151.5
AN Reportable Segment, Import [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	106.8
AN Reportable Segment, Premium Luxury [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	$ 308.2