Segment Information (Details) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2025 USD ($)		Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) segments	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segments					4
Revenues from external customers		$ 7,037.4		$ 6,586.1	$ 20,702.2	$ 19,552.2
Cost of sales:
Total cost of sales		5,799.0		5,403.3	16,968.5	16,008.4
Selling, general and administrative expenses:
Total selling, general, and administrative expenses		850.1		811.3	2,526.7	2,430.2
Depreciation and amortization		64.2		61.3	189.9	179.5
Floorplan interest expense		47.5		60.5	139.3	163.8
AutoNation Finance:
AutoNation Finance income (loss)		1.5		(6.2)	3.6	(10.5)
Corporate and other		(42.5)		(39.9)	(362.2)	(199.6)
Other interest expense		(45.1)		(44.9)	(133.6)	(136.3)
Other income, net		7.8		2.1	6.9	9.0
INCOME BEFORE INCOME TAXES		287.6		247.4	660.0	674.9
Segment assets		14,200.5			14,200.5		$ 13,001.7
New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		3,415.6		3,171.2	10,060.0	9,273.0
Cost of sales:
Total cost of sales		3,264.6		2,994.1	9,550.7	8,709.6
Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		2,015.7		1,901.4	5,923.1	5,808.6
Cost of sales:
Total cost of sales		1,900.8		1,790.2	5,558.3	5,474.5
Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		1,226.2		1,170.9	3,611.3	3,460.4
Cost of sales:
Total cost of sales		629.2		612.7	1,848.0	1,809.8
Other
Segment Reporting Information [Line Items]
Revenues from external customers		5.1		7.2	12.8	16.1
Cost of sales:
Total cost of sales		4.4		6.3	11.5	14.5
AN Reportable Segments
Segment Reporting Information [Line Items]
Revenues from external customers		6,677.8		6,247.1	19,643.6	18,554.8
AN Reportable Segment, Domestic
Segment Reporting Information [Line Items]
Revenues from external customers		1,945.3		1,774.9	5,583.2	5,271.0
AN Reportable Segment, Domestic | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,001.4		872.5	2,846.7	2,528.8
AN Reportable Segment, Domestic | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		531.0		507.2	1,544.3	1,566.4
AN Reportable Segment, Domestic | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		293.6		290.8	851.9	875.9
AN Reportable Segment, Domestic | Other
Segment Reporting Information [Line Items]
Revenues from external customers		0.9		3.2	1.6	4.9
AN Reportable Segment, Import
Segment Reporting Information [Line Items]
Revenues from external customers		2,173.1		2,046.2	6,368.7	6,044.5
AN Reportable Segment, Import | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,145.3		1,078.0	3,336.9	3,152.1
AN Reportable Segment, Import | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		561.5		543.3	1,657.8	1,645.1
AN Reportable Segment, Import | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		337.5		307.1	999.1	891.2
AN Reportable Segment, Import | Other
Segment Reporting Information [Line Items]
Revenues from external customers		2.8		2.4	6.7	6.3
AN Reportable Segment, Premium Luxury
Segment Reporting Information [Line Items]
Revenues from external customers		2,559.4		2,426.0	7,691.7	7,239.3
AN Reportable Segment, Premium Luxury | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,268.9		1,220.7	3,876.4	3,592.1
AN Reportable Segment, Premium Luxury | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		737.6		679.3	2,172.0	2,103.2
AN Reportable Segment, Premium Luxury | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		440.9		422.8	1,302.7	1,237.3
AN Reportable Segment, Premium Luxury | Other
Segment Reporting Information [Line Items]
Revenues from external customers		0.2		0.0	0.4	0.3
AN Reportable Segment, AN Finance
AutoNation Finance:
Interest and fee income		55.2		32.9	145.7	81.2
Interest expense		(21.2)		(11.4)	(52.9)	(27.1)
Provision for credit losses		(22.0)		(18.4)	(60.1)	(36.3)
Direct expenses		(10.5)		(9.3)	(29.1)	(28.3)
AutoNation Finance income (loss)		1.5		(6.2)	3.6	(10.5)
Operating Segments | AN Reportable Segment, Franchised Dealerships
Selling, general and administrative expenses:
Franchised dealerships - segment income		365.9		336.3	1,145.3	1,012.3
Operating Segments | AN Reportable Segment, Domestic
Segment Reporting Information [Line Items]
Revenues from external customers		1,945.3		1,774.9	5,583.2	5,271.0
Cost of sales:
Total cost of sales		1,640.8		1,486.8	4,685.2	4,403.6
Selling, general and administrative expenses:
Compensation		127.0		122.5	379.3	378.3
Advertising		17.7		18.2	51.1	50.8
Store overhead		48.8		51.0	139.7	153.4
Total selling, general, and administrative expenses		193.5		191.7	570.1	582.5
Depreciation and amortization		11.6		11.1	34.1	33.3
Floorplan interest expense		18.1		22.9	51.5	63.8
Other income		0.0	[1]		0.0	(0.1)
Franchised dealerships - segment income		81.3		62.4	242.3	187.9
AutoNation Finance:
Segment assets	[2]	2,379.4			2,379.4		2,297.9
Operating Segments | AN Reportable Segment, Domestic | New vehicle
Cost of sales:
Total cost of sales		980.5		841.7	2,767.9	2,419.6
Operating Segments | AN Reportable Segment, Domestic | Used vehicle
Cost of sales:
Total cost of sales		505.5		481.7	1,463.0	1,494.4
Operating Segments | AN Reportable Segment, Domestic | Parts and service
Cost of sales:
Total cost of sales		154.5		160.6	454.0	485.8
Operating Segments | AN Reportable Segment, Domestic | Other
Cost of sales:
Total cost of sales		0.3		2.8	0.3	3.8
Operating Segments | AN Reportable Segment, Import
Segment Reporting Information [Line Items]
Revenues from external customers		2,173.1		2,046.2	6,368.7	6,044.5
Cost of sales:
Total cost of sales		1,794.4		1,686.2	5,228.1	4,968.3
Selling, general and administrative expenses:
Compensation		151.1		142.4	456.9	432.8
Advertising		24.4		21.9	69.3	61.4
Store overhead		56.9		54.8	165.5	163.7
Total selling, general, and administrative expenses		232.4		219.1	691.7	657.9
Depreciation and amortization		12.8		11.1	37.6	32.6
Floorplan interest expense		9.9		10.6	28.1	29.5
Other income		(0.1)	[1]		(0.1)	0.0
Franchised dealerships - segment income		123.7		119.2	383.3	356.2
AutoNation Finance:
Segment assets	[2]	2,131.3			2,131.3		2,029.8
Operating Segments | AN Reportable Segment, Import | New vehicle
Cost of sales:
Total cost of sales		1,091.5		1,016.6	3,164.1	2,962.1
Operating Segments | AN Reportable Segment, Import | Used vehicle
Cost of sales:
Total cost of sales		526.0		508.2	1,549.6	1,541.5
Operating Segments | AN Reportable Segment, Import | Parts and service
Cost of sales:
Total cost of sales		172.8		158.1	503.6	454.8
Operating Segments | AN Reportable Segment, Import | Other
Cost of sales:
Total cost of sales		4.1		3.3	10.8	9.9
Operating Segments | AN Reportable Segment, Premium Luxury
Segment Reporting Information [Line Items]
Revenues from external customers		2,559.4		2,426.0	7,691.7	7,239.3
Cost of sales:
Total cost of sales		2,103.3		1,980.5	6,283.6	5,901.1
Selling, general and administrative expenses:
Compensation		159.6		155.6	493.5	476.6
Advertising		17.2		14.0	48.2	38.8
Store overhead		79.5		75.9	231.2	229.5
Total selling, general, and administrative expenses		256.3		245.5	772.9	744.9
Depreciation and amortization		20.6		19.9	60.6	59.6
Floorplan interest expense		18.3		25.4	55.0	65.5
Other income		0.0	[1]		(0.1)	0.0
Franchised dealerships - segment income		160.9		154.7	519.7	468.2
AutoNation Finance:
Segment assets	[2]	3,626.3			3,626.3		3,696.0
Operating Segments | AN Reportable Segment, Premium Luxury | New vehicle
Cost of sales:
Total cost of sales		1,192.7		1,135.5	3,618.8	3,327.5
Operating Segments | AN Reportable Segment, Premium Luxury | Used vehicle
Cost of sales:
Total cost of sales		700.2		644.6	2,049.0	1,989.8
Operating Segments | AN Reportable Segment, Premium Luxury | Parts and service
Cost of sales:
Total cost of sales		210.3		200.5	615.6	583.8
Operating Segments | AN Reportable Segment, Premium Luxury | Other
Cost of sales:
Total cost of sales		0.1		(0.1)	0.2	0.0
Operating Segments | AN Reportable Segment, AN Finance
AutoNation Finance:
Interest and fee income		55.2		32.9	145.7	81.2
Interest expense		(21.2)		(11.4)	(52.9)	(27.1)
Provision for credit losses		(22.0)		(18.4)	(60.1)	(36.3)
Direct expenses		(10.5)		(9.3)	(29.1)	(28.3)
AutoNation Finance income (loss)		1.5		(6.2)	3.6	(10.5)
Segment assets	[2]	2,000.7			2,000.7		$ 1,114.4
Corporate and other
Segment Reporting Information [Line Items]
Revenues from external customers		$ 359.6		$ 339.0	$ 1,058.6	$ 997.4

[1] (2) Other income includes net gains on asset dispositions.

[2] (1) Excludes capital expenditures for active construction projects, which are reflected in segment assets upon completion of the related project.