Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues		$ 21,335.7		$ 21,412.8		$ 21,534.6
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		18,604.7		18,759.5
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	2,731.0		2,653.3
New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		11,166.5		11,751.6		12,180.8
Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		5,466.5		5,123.3		4,878.4
Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		3,572.1		3,447.6		3,398.3
Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,023.3		981.4		939.2
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		107.3		108.9		137.9
AN Reportable Segment, Domestic [Member]
Disaggregation of Revenue [Line Items]
Revenues		6,671.4		7,134.5		7,452.8
AN Reportable Segment, Domestic [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		5,969.6		6,441.2
AN Reportable Segment, Domestic [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	701.8		693.3
AN Reportable Segment, Domestic [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		3,502.5		3,900.8
AN Reportable Segment, Domestic [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,769.5		1,725.2
AN Reportable Segment, Domestic [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		959.0		1,082.8
AN Reportable Segment, Domestic [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		354.6		344.4
AN Reportable Segment, Domestic [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		85.8		81.3
AN Reportable Segment, Import [Member]
Disaggregation of Revenue [Line Items]
Revenues		6,468.7		6,786.4		6,873.4
AN Reportable Segment, Import [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		5,768.3		6,079.1
AN Reportable Segment, Import [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	700.4		707.3
AN Reportable Segment, Import [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		3,695.6		4,046.4
AN Reportable Segment, Import [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,501.9		1,418.7
AN Reportable Segment, Import [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		889.7		934.8
AN Reportable Segment, Import [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		368.3		362.6
AN Reportable Segment, Import [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		13.2		23.9
AN Reportable Segment, Premium Luxury [Member]
Disaggregation of Revenue [Line Items]
Revenues		7,434.8		7,010.9		6,832.7
AN Reportable Segment, Premium Luxury [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		6,467.5		6,098.3
AN Reportable Segment, Premium Luxury [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	967.3		912.6
AN Reportable Segment, Premium Luxury [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		3,968.4		3,804.4
AN Reportable Segment, Premium Luxury [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		2,045.6		1,875.1
AN Reportable Segment, Premium Luxury [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,136.0		1,082.2
AN Reportable Segment, Premium Luxury [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		279.2		246.0
AN Reportable Segment, Premium Luxury [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		5.6		3.2
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		760.8	[2]	481.0	[2]	$ 375.7
Corporate and Other [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	399.3		140.9
Corporate and Other [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1],[2]	361.5		340.1
Corporate and Other [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	0.0		0.0
Corporate and Other [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	149.5		104.3
Corporate and Other [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	587.4		347.8
Corporate and Other [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	21.2		28.4
Corporate and Other [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 2.7		$ 0.5

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

[2] “Corporate and other” is comprised of our other businesses, including collision centers, auction operations, AutoNation USA stand-alone used vehicle sales and service centers, and aftermarket collision parts businesses.