Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 25,844.0	$ 20,390.0	$ 21,335.7
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	23,072.9	17,900.4	18,604.7
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,771.1	2,489.6	2,731.0
New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	12,081.7	10,418.6	11,166.5
Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,638.8	5,601.3	5,466.5
Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,706.6	3,257.4	3,572.1
Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,384.5	1,059.3	1,023.3
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	32.4	53.4	107.3
AN Reportable Segment, Domestic [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,959.9	6,490.6	6,671.4
AN Reportable Segment, Domestic [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,260.7	5,841.6	5,969.6
AN Reportable Segment, Domestic [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	699.2	649.0	701.8
AN Reportable Segment, Domestic [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,601.8	3,411.1	3,502.5
AN Reportable Segment, Domestic [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,875.0	1,781.4	1,769.5
AN Reportable Segment, Domestic [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,007.6	891.5	959.0
AN Reportable Segment, Domestic [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	469.1	370.5	354.6
AN Reportable Segment, Domestic [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	6.4	36.1	85.8
AN Reportable Segment, Import [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,798.5	5,988.0	6,468.7
AN Reportable Segment, Import [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,079.0	5,343.8	5,768.3
AN Reportable Segment, Import [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	719.5	644.2	700.4
AN Reportable Segment, Import [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,969.8	3,283.7	3,695.6
AN Reportable Segment, Import [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,370.5	1,516.5	1,501.9
AN Reportable Segment, Import [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	950.0	811.3	889.7
AN Reportable Segment, Import [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	489.6	361.7	368.3
AN Reportable Segment, Import [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	18.6	14.8	13.2
AN Reportable Segment, Premium Luxury [Member]
Disaggregation of Revenue [Line Items]
Revenues	9,229.9	7,202.8	7,434.8
AN Reportable Segment, Premium Luxury [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,197.6	6,301.3	6,467.5
AN Reportable Segment, Premium Luxury [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,032.3	901.5	967.3
AN Reportable Segment, Premium Luxury [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,510.1	3,723.8	3,968.4
AN Reportable Segment, Premium Luxury [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,067.4	2,125.9	2,045.6
AN Reportable Segment, Premium Luxury [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,246.7	1,058.1	1,136.0
AN Reportable Segment, Premium Luxury [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	401.0	294.7	279.2
AN Reportable Segment, Premium Luxury [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	4.7	0.3	5.6
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	855.7	708.6	760.8
Corporate and Other [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	535.6	413.7	399.3
Corporate and Other [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	320.1	294.9	361.5
Corporate and Other [Member] | New Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Corporate and Other [Member] | Used Vehicle [Member]
Disaggregation of Revenue [Line Items]
Revenues	325.9	177.5	149.5
Corporate and Other [Member] | Parts and Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	502.3	496.5	587.4
Corporate and Other [Member] | Finance and Insurance, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	24.8	32.4	21.2
Corporate and Other [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 2.7	$ 2.2	$ 2.7