Goodwill and Intangible Assets, Net (Goodwill) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Goodwill [Roll Forward]
Goodwill, gross, beginning balance				$ 3,381.2
Accumulated impairment losses, beginning balance				(1,928.3)
Goodwill, beginning balance				1,452.9
Acquisitions, dispositions, and other adjustments, net	[1]			11.9
Impairment		$ 0.0	$ 0.0	(65.3)	$ 0.0
Goodwill, gross, ending balance		3,393.1		3,393.1
Accumulated impairment losses, ending balance		(1,993.6)		(1,993.6)
Goodwill, ending balance		1,399.5		1,399.5
Reporting Unit, Domestic
Goodwill [Roll Forward]
Goodwill, gross, beginning balance				363.4
Accumulated impairment losses, beginning balance				(140.0)
Goodwill, beginning balance				223.4
Acquisitions, dispositions, and other adjustments, net	[1]			(1.5)
Impairment				0.0
Goodwill, gross, ending balance		361.9		361.9
Accumulated impairment losses, ending balance		(140.0)		(140.0)
Goodwill, ending balance		221.9		221.9
Reporting Unit, Import
Goodwill [Roll Forward]
Goodwill, gross, beginning balance				524.3
Accumulated impairment losses, beginning balance				0.0
Goodwill, beginning balance				524.3
Acquisitions, dispositions, and other adjustments, net	[1]			(0.9)
Impairment				0.0
Goodwill, gross, ending balance		523.4		523.4
Accumulated impairment losses, ending balance		0.0		0.0
Goodwill, ending balance		523.4		523.4
Reporting Unit, Premium Luxury
Goodwill [Roll Forward]
Goodwill, gross, beginning balance				739.1
Accumulated impairment losses, beginning balance				(257.4)
Goodwill, beginning balance				481.7
Acquisitions, dispositions, and other adjustments, net	[1]			14.3
Impairment				0.0
Goodwill, gross, ending balance		753.4		753.4
Accumulated impairment losses, ending balance		(257.4)		(257.4)
Goodwill, ending balance		496.0		496.0
Reporting Unit, AN Finance
Goodwill [Roll Forward]
Goodwill, gross, beginning balance				78.4
Accumulated impairment losses, beginning balance				0.0
Goodwill, beginning balance				78.4
Acquisitions, dispositions, and other adjustments, net	[1]			0.0
Impairment				0.0
Goodwill, gross, ending balance		78.4		78.4
Accumulated impairment losses, ending balance		0.0		0.0
Goodwill, ending balance		78.4		78.4
Reporting Unit, Other
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	[2]			1,676.0
Accumulated impairment losses, beginning balance	[2]			(1,530.9)
Goodwill, beginning balance				145.1
Acquisitions, dispositions, and other adjustments, net	[1]			0.0
Impairment				(65.3)
Goodwill, gross, ending balance	[2]	1,676.0		1,676.0
Accumulated impairment losses, ending balance	[2]	(1,596.2)		(1,596.2)
Goodwill, ending balance		79.8		79.8
Single Reporting Unit (before change in reporting units)
Goodwill [Roll Forward]
Accumulated impairment losses, ending balance		$ (1,470.0)		$ (1,470.0)

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

[2] Gross goodwill balance and accumulated impairment losses reflected in “Other” include $1.47 billion associated with our single reporting unit (prior to September 30, 2008, our reporting unit reporting structure was comprised of a single reporting unit). Gross goodwill balance reflected in “Other” also includes amounts associated with the Collision Center, Parts Center, and AutoNation Mobile Service reporting units, as applicable in a given period.