Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues		$ 4,533.0	$ 5,343.8	$ 9,200.0	$ 10,325.6
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		4,001.2	4,650.1	8,002.6	8,962.9
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	531.8	693.7	1,197.4	1,362.7
New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		2,261.3	2,769.6	4,543.2	5,266.3
Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,324.5	1,379.4	2,573.2	2,719.0
Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		689.9	901.5	1,566.2	1,778.2
Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		246.4	255.2	482.2	491.7
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		10.9	38.1	35.2	70.4
AN Reportable Segment, Domestic [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,486.0	1,707.3	2,969.5	3,276.1
AN Reportable Segment, Domestic [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,343.2	1,528.4	2,654.6	2,926.5
AN Reportable Segment, Domestic [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	142.8	178.9	314.9	349.6
AN Reportable Segment, Domestic [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		761.7	894.5	1,500.6	1,675.5
AN Reportable Segment, Domestic [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		436.8	447.0	841.4	890.4
AN Reportable Segment, Domestic [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		193.3	241.2	428.9	477.5
AN Reportable Segment, Domestic [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		88.0	89.8	171.1	170.2
AN Reportable Segment, Domestic [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		6.2	34.8	27.5	62.5
AN Reportable Segment, Import [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,325.3	1,627.3	2,687.4	3,123.4
AN Reportable Segment, Import [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,187.0	1,445.3	2,387.5	2,770.1
AN Reportable Segment, Import [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	138.3	182.0	299.9	353.3
AN Reportable Segment, Import [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		712.6	916.1	1,446.5	1,736.3
AN Reportable Segment, Import [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		355.8	388.0	690.3	757.5
AN Reportable Segment, Import [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		170.4	229.2	377.9	449.4
AN Reportable Segment, Import [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		82.4	91.4	166.4	175.9
AN Reportable Segment, Import [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		4.1	2.6	6.3	4.3
AN Reportable Segment, Premium Luxury [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,564.8	1,820.9	3,181.6	3,555.0
AN Reportable Segment, Premium Luxury [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,373.6	1,577.7	2,753.8	3,074.9
AN Reportable Segment, Premium Luxury [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	191.2	243.2	427.8	480.1
AN Reportable Segment, Premium Luxury [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		787.0	959.0	1,596.1	1,854.5
AN Reportable Segment, Premium Luxury [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		490.3	507.8	957.6	1,004.5
AN Reportable Segment, Premium Luxury [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		223.2	285.7	500.6	563.9
AN Reportable Segment, Premium Luxury [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		64.3	68.4	127.3	130.0
AN Reportable Segment, Premium Luxury [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		0.0	0.0	0.0	2.1
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	156.9	188.3	361.5	371.1
Corporate and Other [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	97.4	98.7	206.7	191.4
Corporate and Other [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1],[2]	59.5	89.6	154.8	179.7
Corporate and Other [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	0.0	0.0	0.0	0.0
Corporate and Other [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	41.6	36.6	83.9	66.6
Corporate and Other [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	103.0	145.4	258.8	287.4
Corporate and Other [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	11.7	5.6	17.4	15.6
Corporate and Other [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 0.6	$ 0.7	$ 1.4	$ 1.5

[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 parts distribution centers.