Segment Information (Details) $ in Millions		3 Months Ended
		Mar. 31, 2026 USD ($) segments	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segments		4
Revenues from external customers		$ 6,552.1	$ 6,690.4
Cost of sales:
Total cost of sales		5,341.0	5,470.5
Selling, general and administrative expenses:
Total selling, general, and administrative expenses		842.2	821.9
Depreciation and amortization		63.0	61.8
Floorplan interest expense		41.8	46.5
AutoNation Finance:
AutoNation Finance income		9.4	0.1
Corporate and other		(83.6)	(84.5)
Other interest expense		(48.0)	(42.3)
Other income, net		51.2	(13.2)
INCOME BEFORE INCOME TAXES		275.7	234.0
Segment assets		14,623.3		$ 14,392.2
New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		3,011.0	3,248.1
Cost of sales:
Total cost of sales		2,866.5	3,073.2
Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,963.8	1,922.4
Cost of sales:
Total cost of sales		1,842.4	1,797.9
Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		1,220.9	1,164.0
Cost of sales:
Total cost of sales		627.5	596.3
Other
Segment Reporting Information [Line Items]
Revenues from external customers		4.4	3.4
Cost of sales:
Total cost of sales		4.6	3.1
AN Reportable Segments
Segment Reporting Information [Line Items]
Revenues from external customers		6,206.2	6,341.2
AN Reportable Segment, Domestic
Segment Reporting Information [Line Items]
Revenues from external customers		1,716.6	1,717.4
AN Reportable Segment, Domestic | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		826.8	860.2
AN Reportable Segment, Domestic | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		499.4	486.1
AN Reportable Segment, Domestic | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		282.0	269.0
AN Reportable Segment, Domestic | Other
Segment Reporting Information [Line Items]
Revenues from external customers		0.8	0.3
AN Reportable Segment, Import
Segment Reporting Information [Line Items]
Revenues from external customers		2,048.1	2,047.3
AN Reportable Segment, Import | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,035.3	1,062.0
AN Reportable Segment, Import | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		554.0	546.7
AN Reportable Segment, Import | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		334.5	318.6
AN Reportable Segment, Import | Other
Segment Reporting Information [Line Items]
Revenues from external customers		2.0	1.5
AN Reportable Segment, Premium Luxury
Segment Reporting Information [Line Items]
Revenues from external customers		2,441.5	2,576.5
AN Reportable Segment, Premium Luxury | New vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		1,148.9	1,325.9
AN Reportable Segment, Premium Luxury | Used vehicle
Segment Reporting Information [Line Items]
Revenues from external customers		734.2	712.1
AN Reportable Segment, Premium Luxury | Parts and service
Segment Reporting Information [Line Items]
Revenues from external customers		454.4	424.4
AN Reportable Segment, Premium Luxury | Other
Segment Reporting Information [Line Items]
Revenues from external customers		0.4	0.0
AN Reportable Segment, AN Finance
AutoNation Finance:
Interest and fee income		62.7	41.9
Interest expense		(24.4)	(13.9)
Provision for credit losses		(19.5)	(18.9)
Direct expenses	[1]	(9.4)	(9.0)
AutoNation Finance income		9.4	0.1
Operating Segments | AN Reportable Segment, Franchised Dealerships
Selling, general and administrative expenses:
Franchised dealerships - segment income		346.7	373.9
Operating Segments | AN Reportable Segment, Domestic
Segment Reporting Information [Line Items]
Revenues from external customers		1,716.6	1,717.4
Cost of sales:
Total cost of sales		1,423.6	1,438.9
Selling, general and administrative expenses:
Compensation		122.1	119.8
Advertising		18.1	16.7
Store overhead		48.0	45.4
Total selling, general, and administrative expenses		188.2	181.9
Depreciation and amortization		11.2	11.0
Floorplan interest expense		15.5	16.6
Other income	[2]		0.0
Franchised dealerships - segment income		78.1	69.0
AutoNation Finance:
Segment assets	[3]	2,315.3		2,360.0
Operating Segments | AN Reportable Segment, Domestic | New vehicle
Cost of sales:
Total cost of sales		804.6	834.6
Operating Segments | AN Reportable Segment, Domestic | Used vehicle
Cost of sales:
Total cost of sales		471.5	459.0
Operating Segments | AN Reportable Segment, Domestic | Parts and service
Cost of sales:
Total cost of sales		147.1	145.3
Operating Segments | AN Reportable Segment, Domestic | Other
Cost of sales:
Total cost of sales		0.4	0.0
Operating Segments | AN Reportable Segment, Import
Segment Reporting Information [Line Items]
Revenues from external customers		2,048.1	2,047.3
Cost of sales:
Total cost of sales		1,680.7	1,676.9
Selling, general and administrative expenses:
Compensation		149.3	148.4
Advertising		26.3	21.6
Store overhead		55.9	53.5
Total selling, general, and administrative expenses		231.5	223.5
Depreciation and amortization		13.6	12.0
Floorplan interest expense		8.5	8.7
Other income	[2]		0.0
Franchised dealerships - segment income		113.8	126.2
AutoNation Finance:
Segment assets	[3]	2,176.3		2,209.3
Operating Segments | AN Reportable Segment, Import | New vehicle
Cost of sales:
Total cost of sales		986.4	1,004.8
Operating Segments | AN Reportable Segment, Import | Used vehicle
Cost of sales:
Total cost of sales		516.8	510.1
Operating Segments | AN Reportable Segment, Import | Parts and service
Cost of sales:
Total cost of sales		173.8	159.2
Operating Segments | AN Reportable Segment, Import | Other
Cost of sales:
Total cost of sales		3.7	2.8
Operating Segments | AN Reportable Segment, Premium Luxury
Segment Reporting Information [Line Items]
Revenues from external customers		2,441.5	2,576.5
Cost of sales:
Total cost of sales		1,986.2	2,102.0
Selling, general and administrative expenses:
Compensation		162.6	165.7
Advertising		18.0	15.8
Store overhead		82.2	75.5
Total selling, general, and administrative expenses		262.8	257.0
Depreciation and amortization		21.3	19.9
Floorplan interest expense		16.4	19.0
Other income	[2]		(0.1)
Franchised dealerships - segment income		154.8	178.7
AutoNation Finance:
Segment assets	[3]	3,624.4		3,611.2
Operating Segments | AN Reportable Segment, Premium Luxury | New vehicle
Cost of sales:
Total cost of sales		1,075.6	1,233.7
Operating Segments | AN Reportable Segment, Premium Luxury | Used vehicle
Cost of sales:
Total cost of sales		695.1	669.0
Operating Segments | AN Reportable Segment, Premium Luxury | Parts and service
Cost of sales:
Total cost of sales		215.2	199.4
Operating Segments | AN Reportable Segment, Premium Luxury | Other
Cost of sales:
Total cost of sales		0.3	(0.1)
Operating Segments | AN Reportable Segment, AN Finance
AutoNation Finance:
Interest and fee income		62.7	41.9
Interest expense		(24.4)	(13.9)
Provision for credit losses		(19.5)	(18.9)
Direct expenses		(9.4)	(9.0)
AutoNation Finance income		9.4	0.1
Segment assets	[3]	2,449.6		$ 2,185.7
Corporate and other
Segment Reporting Information [Line Items]
Revenues from external customers		$ 345.9	$ 349.2

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

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

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