Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 12,672.7	$ 11,821.4	$ 10,086.5
Cost of sales:
Total cost of sales	10,718.9	10,044.4	8,570.4
Gross profit	1,953.8	1,777.0	1,516.1
Asset impairments	2.6	1.3	0.0
Selling, general and administrative	1,373.8	1,253.3	1,049.4
Depreciation and amortization	82.4	75.4	57.7
Operating income	495.0	447.0	409.0
Floor plan interest expense	(72.8)	(62.3)	(39.3)
Other interest expense	(60.6)	(56.0)	(34.8)
Other income, net	13.8	8.8	12.2
Income before income taxes	375.4	337.5	347.1
Income tax provision	(103.9)	(71.8)	(101.9)
Net income	$ 271.5	$ 265.7	$ 245.2
Basic net income per share (in dollars per share)	$ 11.70	$ 10.91	$ 9.78
Shares used in basic per share calculations	23.2	24.4	25.1
Diluted net income per share (in dollars per share)	$ 11.60	$ 10.86	$ 9.75
Shares used in diluted per share calculations	23.4	24.5	25.1
Cash dividend paid per Class A and Class B share (in dollars per share)	$ 1.19	$ 1.14	$ 1.06
New vehicle
Revenues:
Total revenues	$ 6,799.1	$ 6,602.8	$ 5,763.6
Cost of sales:
Total cost of sales	6,413.5	6,217.7	5,423.8
Used vehicle retail
Revenues:
Total revenues	3,527.2	3,079.0	2,544.4
Cost of sales:
Total cost of sales	3,159.6	2,756.1	2,257.6
Used vehicle wholesale
Revenues:
Total revenues	301.2	331.3	277.8
Cost of sales:
Total cost of sales	297.5	325.8	273.0
Finance and insurance
Revenues:
Total revenues	518.6	454.8	385.9
Service, body and parts
Revenues:
Total revenues	1,325.1	1,222.3	1,015.8
Cost of sales:
Total cost of sales	657.5	621.6	522.7
Fleet and other
Revenues:
Total revenues	201.5	131.2	99.0
Cost of sales:
Total cost of sales	$ 190.8	$ 123.2	$ 93.3