Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ 5,461.2	$ 5,349.2	$ 15,786.8	$ 16,001.1
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		4,768.6	4,681.6	13,731.7	14,014.0
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	692.6	667.6	2,055.1	1,987.1
New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		2,874.8	2,933.1	8,141.1	8,685.0
Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,402.9	1,281.7	4,121.9	3,910.9
Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		902.6	864.0	2,680.8	2,579.6
Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		266.2	247.4	757.9	736.0
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		14.7	23.0	85.1	89.6
AN Reportable Segment, Domestic [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,728.6	1,789.7	5,004.7	5,389.5
AN Reportable Segment, Domestic [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,547.1	1,613.5	4,473.6	4,870.0
AN Reportable Segment, Domestic [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	181.5	176.2	531.1	519.5
AN Reportable Segment, Domestic [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		925.4	988.5	2,600.9	2,913.7
AN Reportable Segment, Domestic [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		456.6	424.4	1,347.0	1,334.4
AN Reportable Segment, Domestic [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		244.7	271.6	722.2	810.8
AN Reportable Segment, Domestic [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		95.1	88.6	265.3	263.2
AN Reportable Segment, Domestic [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		6.8	16.6	69.3	67.4
AN Reportable Segment, Import [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,722.5	1,770.6	4,845.9	5,140.2
AN Reportable Segment, Import [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,543.1	1,591.6	4,313.3	4,603.3
AN Reportable Segment, Import [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	179.4	179.0	532.6	536.9
AN Reportable Segment, Import [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,003.8	1,070.3	2,740.1	3,045.0
AN Reportable Segment, Import [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		386.4	365.3	1,143.9	1,092.3
AN Reportable Segment, Import [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		226.1	235.8	675.5	707.1
AN Reportable Segment, Import [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		99.9	94.4	275.8	275.8
AN Reportable Segment, Import [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		6.3	4.8	10.6	20.0
AN Reportable Segment, Premium Luxury [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,820.5	1,668.8	5,375.5	5,116.8
AN Reportable Segment, Premium Luxury [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,579.0	1,441.5	4,654.0	4,440.5
AN Reportable Segment, Premium Luxury [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	241.5	227.3	721.5	676.3
AN Reportable Segment, Premium Luxury [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		945.6	874.3	2,800.1	2,726.3
AN Reportable Segment, Premium Luxury [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues		519.7	463.6	1,524.2	1,405.9
AN Reportable Segment, Premium Luxury [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues		283.8	269.4	847.7	804.1
AN Reportable Segment, Premium Luxury [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues		70.0	60.0	200.0	178.6
AN Reportable Segment, Premium Luxury [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues		1.4	1.5	3.5	1.9
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	189.6	120.1	560.7	354.6
Corporate and Other [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	99.4	35.0	290.8	100.2
Corporate and Other [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1],[2]	90.2	85.1	269.9	254.4
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]	40.2	28.4	106.8	78.3
Corporate and Other [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	148.0	87.2	435.4	257.6
Corporate and Other [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	1.2	4.4	16.8	18.4
Corporate and Other [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 0.2	$ 0.1	$ 1.7	$ 0.3

[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.