Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2023		Jun. 30, 2022		Jun. 30, 2023		Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenues		$ 6,890.1		$ 6,869.2		$ 13,288.8		$ 13,622.0
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues		6,000.5		6,088.5		11,570.8		12,095.9
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues		889.6	[1]	780.7	[1]	1,718.0	[2]	1,526.1	[2]
New vehicle
Disaggregation of Revenue [Line Items]
Revenues		3,281.0		2,935.8		6,212.9		5,743.0
Used vehicle
Disaggregation of Revenue [Line Items]
Revenues		2,088.0		2,520.4		4,120.6		5,092.8
Parts and service
Disaggregation of Revenue [Line Items]
Revenues		1,145.3		1,036.3		2,235.1		2,040.2
Finance and insurance, net
Disaggregation of Revenue [Line Items]
Revenues		369.5		367.6		701.9		731.5
Other
Disaggregation of Revenue [Line Items]
Revenues		6.3		9.1		18.3		14.5
Domestic
Disaggregation of Revenue [Line Items]
Revenues		1,955.5		2,040.9		3,786.6		4,075.3
Domestic | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues		1,740.1		1,848.7		3,369.4		3,699.3
Domestic | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues		215.4	[1]	192.2	[1]	417.2	[2]	376.0	[2]
Domestic | New vehicle
Disaggregation of Revenue [Line Items]
Revenues		923.0		858.1		1,751.0		1,680.6
Domestic | Used vehicle
Disaggregation of Revenue [Line Items]
Revenues		619.0		786.8		1,231.3		1,609.9
Domestic | Parts and service
Disaggregation of Revenue [Line Items]
Revenues		298.7		275.5		586.3		544.2
Domestic | Finance and insurance, net
Disaggregation of Revenue [Line Items]
Revenues		114.3		119.4		216.6		238.6
Domestic | Other
Disaggregation of Revenue [Line Items]
Revenues		0.5		1.1		1.4		2.0
Import
Disaggregation of Revenue [Line Items]
Revenues		1,997.7		1,949.7		3,787.0		3,923.8
Import | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues		1,771.5		1,748.9		3,358.4		3,532.8
Import | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues		226.2	[1]	200.8	[1]	428.6	[2]	391.0	[2]
Import | New vehicle
Disaggregation of Revenue [Line Items]
Revenues		1,011.2		852.4		1,867.6		1,734.0
Import | Used vehicle
Disaggregation of Revenue [Line Items]
Revenues		563.2		699.6		1,105.3		1,407.2
Import | Parts and service
Disaggregation of Revenue [Line Items]
Revenues		291.3		266.3		559.7		521.8
Import | Finance and insurance, net
Disaggregation of Revenue [Line Items]
Revenues		128.0		125.7		240.4		252.1
Import | Other
Disaggregation of Revenue [Line Items]
Revenues		4.0		5.7		14.0		8.7
Premium Luxury
Disaggregation of Revenue [Line Items]
Revenues		2,620.5		2,616.6		5,105.4		5,095.3
Premium Luxury | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues		2,278.3		2,311.4		4,437.7		4,497.7
Premium Luxury | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues		342.2	[1]	305.2	[1]	667.7	[2]	597.6	[2]
Premium Luxury | New vehicle
Disaggregation of Revenue [Line Items]
Revenues		1,346.8		1,225.3		2,594.3		2,328.4
Premium Luxury | Used vehicle
Disaggregation of Revenue [Line Items]
Revenues		756.9		904.6		1,502.7		1,820.7
Premium Luxury | Parts and service
Disaggregation of Revenue [Line Items]
Revenues		400.3		367.0		786.5		718.9
Premium Luxury | Finance and insurance, net
Disaggregation of Revenue [Line Items]
Revenues		115.8		118.4		220.8		225.6
Premium Luxury | Other
Disaggregation of Revenue [Line Items]
Revenues		0.7		1.3		1.1		1.7
Corporate and other
Disaggregation of Revenue [Line Items]
Revenues	[3]	316.4		262.0		609.8		527.6
Corporate and other | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	[3]	210.6		179.5		405.3		366.1
Corporate and other | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	[3]	105.8	[1]	82.5	[1]	204.5	[2]	161.5	[2]
Corporate and other | New vehicle
Disaggregation of Revenue [Line Items]
Revenues	[3]	0.0		0.0		0.0		0.0
Corporate and other | Used vehicle
Disaggregation of Revenue [Line Items]
Revenues	[3]	148.9		129.4		281.3		255.0
Corporate and other | Parts and service
Disaggregation of Revenue [Line Items]
Revenues	[3]	155.0		127.5		302.6		255.3
Corporate and other | Finance and insurance, net
Disaggregation of Revenue [Line Items]
Revenues	[3]	11.4		4.1		24.1		15.2
Corporate and other | Other
Disaggregation of Revenue [Line Items]
Revenues	[3]	$ 1.1		$ 1.0		$ 1.8		$ 2.1

[1] (2) Represents revenue recognized during the period for automotive repair and maintenance services.

[2] Major Goods/Service Lines

[3] (1) “Corporate and other” is comprised of our other businesses, including AutoNation USA used vehicle stores, collision centers, parts distribution centers, auction operations, and RepairSmith, our mobile automotive repair and maintenance business.