AutoNation Finance Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
AutoNation Finance Income [Line Items]
AutoNation Finance income (loss)	$ 1.5	$ (6.2)	$ 3.6	$ (10.5)
AN Reportable Segment, AN Finance
AutoNation Finance Income [Line Items]
Interest and fee income	55.2	32.9	145.7	81.2
Interest expense	(21.2)	(11.4)	(52.9)	(27.1)
Total interest margin	34.0	21.5	92.8	54.1
Provision for credit losses	(22.0)	(18.4)	(60.1)	(36.3)
Total interest margin after provision for credit losses	12.0	3.1	32.7	17.8
Direct expenses	(10.5)	(9.3)	(29.1)	(28.3)
AutoNation Finance income (loss)	$ 1.5	$ (6.2)	$ 3.6	$ (10.5)