AutoNation Finance Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2026	Mar. 31, 2025
AutoNation Finance Income [Line Items]
AutoNation Finance income		$ 9.4	$ 0.1
AN Reportable Segment, AN Finance
AutoNation Finance Income [Line Items]
Interest and fee income		62.7	41.9
Interest expense		(24.4)	(13.9)
Total interest margin		38.3	28.0
Provision for credit losses		(19.5)	(18.9)
Total interest margin after provision for credit losses		18.8	9.1
Direct expenses	[1]	(9.4)	(9.0)
AutoNation Finance income		$ 9.4	$ 0.1

[1] (1) Direct expenses are comprised primarily of compensation expenses and loan administration costs incurred by our auto finance company.