Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues		$ 4,667.0	$ 4,981.8
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		4,001.5	4,312.8
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	665.5	669.0
New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		2,281.9	2,496.7
Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,248.7	1,339.6
Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		876.3	876.7
Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		235.8	236.5
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		24.3	32.3
AN Reportable Segment, Domestic [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,483.5	1,568.8
AN Reportable Segment, Domestic [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,311.4	1,398.1
AN Reportable Segment, Domestic [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	172.1	170.7
AN Reportable Segment, Domestic [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		738.9	781.0
AN Reportable Segment, Domestic [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		404.6	443.4
AN Reportable Segment, Domestic [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		235.6	236.3
AN Reportable Segment, Domestic [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		83.1	80.4
AN Reportable Segment, Domestic [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		21.3	27.7
AN Reportable Segment, Import [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,362.1	1,496.1
AN Reportable Segment, Import [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,200.5	1,324.8
AN Reportable Segment, Import [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	161.6	171.3
AN Reportable Segment, Import [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		733.9	820.2
AN Reportable Segment, Import [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		334.5	369.5
AN Reportable Segment, Import [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		207.5	220.2
AN Reportable Segment, Import [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		84.0	84.5
AN Reportable Segment, Import [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		2.2	1.7
AN Reportable Segment, Premium Luxury [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,616.8	1,734.1
AN Reportable Segment, Premium Luxury [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,380.2	1,497.2
AN Reportable Segment, Premium Luxury [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	236.6	236.9
AN Reportable Segment, Premium Luxury [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		809.1	895.5
AN Reportable Segment, Premium Luxury [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		467.3	496.7
AN Reportable Segment, Premium Luxury [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		277.4	278.2
AN Reportable Segment, Premium Luxury [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		63.0	61.6
AN Reportable Segment, Premium Luxury [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		0.0	2.1
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	204.6	182.8
Corporate and Other [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	109.4	92.7
Corporate and Other [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1],[2]	95.2	90.1
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]	42.3	30.0
Corporate and Other [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	155.8	142.0
Corporate and Other [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	5.7	10.0
Corporate and Other [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 0.8	$ 0.8

[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 parts distribution centers.