Unaudited Condensed Consolidated Income Statements - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
TOTAL REVENUE	$ 5,903.8	$ 4,667.0
TOTAL COST OF SALES (excluding depreciation shown below)	4,871.0	3,853.8
TOTAL GROSS PROFIT	1,032.8	813.2
Selling, general, and administrative expenses	647.9	600.7
Depreciation and amortization	47.9	48.1
Goodwill impairment	0.0	318.3
Franchise rights impairment	0.0	57.5
Other expense, net	0.1	7.9
OPERATING INCOME (LOSS)	336.9	(219.3)
Non-operating income (expense) items:
Floorplan interest expense	(9.4)	(25.5)
Other interest expense	(21.2)	(23.5)
Other income (loss), net	11.0	(2.9)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	317.3	(271.2)
Income tax provision (benefit)	77.8	(39.0)
NET INCOME (LOSS) FROM CONTINUING OPERATIONS	239.5	(232.2)
Loss from discontinued operations, net of income taxes	(0.1)	(0.1)
NET INCOME (LOSS)	$ 239.4	$ (232.3)
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 2.88	$ (2.58)
Discontinued operations (in dollars per share)	0	0
Net income (loss) (in dollars per share)	$ 2.88	$ (2.58)
Weighted average common shares outstanding (in shares)	83.1	90.0
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 2.85	$ (2.58)
Discontinued operations (in dollars per share)	0	0
Net income (loss) (in dollars per share)	$ 2.85	$ (2.58)
Weighted average common shares outstanding (in shares)	83.9	90.0
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)	80.5	87.2
New Vehicle [Member]
TOTAL REVENUE	$ 2,982.3	$ 2,281.9
TOTAL COST OF SALES (excluding depreciation shown below)	2,792.3	2,185.5
TOTAL GROSS PROFIT	190.0	96.4
Used Vehicle [Member]
TOTAL REVENUE	1,749.1	1,248.7
TOTAL COST OF SALES (excluding depreciation shown below)	1,608.9	1,157.7
TOTAL GROSS PROFIT	140.2	91.0
Parts and Service [Member]
TOTAL REVENUE	851.0	876.3
TOTAL COST OF SALES (excluding depreciation shown below)	462.0	487.5
TOTAL GROSS PROFIT	389.0	388.8
Finance and Insurance, Net [Member]
TOTAL REVENUE	313.0	235.8
TOTAL GROSS PROFIT	313.0	235.8
Product and Service, Other [Member]
TOTAL REVENUE	8.4	24.3
TOTAL COST OF SALES (excluding depreciation shown below)	7.8	23.1
TOTAL GROSS PROFIT	$ 0.6	$ 1.2