Unaudited Condensed Consolidated Income Statements - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Document Fiscal Year Focus			2020
TOTAL REVENUE	$ 5,404.9	$ 5,461.2	$ 14,604.9	$ 15,786.8
TOTAL COST OF SALES (excluding depreciation shown below)	4,433.4	4,573.8	12,025.2	13,159.4
TOTAL GROSS PROFIT	971.5	887.4	2,579.7	2,627.4
Selling, general, and administrative expenses	641.4	653.8	1,790.0	1,913.8
Depreciation and amortization	51.8	45.2	149.0	133.7
Goodwill impairment	0.0	0.0	318.3	0.0
Franchise rights impairment	0.0	0.0	57.5	9.6
Other (income) expense, net	6.6	(5.1)	11.1	(17.5)
OPERATING INCOME	271.7	193.5	253.8	587.8
Non-operating income (expense) items:
Floorplan interest expense	(11.1)	(33.0)	(52.9)	(109.4)
Other interest expense	(23.6)	(26.1)	(70.3)	(81.6)
Interest income	0.1	0.1	0.3	0.4
Other income, net	6.4	2.6	217.9	4.2
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	243.5	137.1	348.8	401.4
Income tax provision	60.9	37.1	118.5	108.3
NET INCOME FROM CONTINUING OPERATIONS	182.6	100.0	230.3	293.1
Loss from discontinued operations, net of income taxes	0.0	(0.5)	(0.2)	(0.8)
NET INCOME	$ 182.6	$ 99.5	$ 230.1	$ 292.3
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 2.07	$ 1.11	$ 2.59	$ 3.25
Discontinued operations (in dollars per share)	0	(0.01)	0	(0.01)
Net income (in dollars per share)	$ 2.07	$ 1.11	$ 2.59	$ 3.24
Weighted average common shares outstanding (in shares)	88.3	89.9	88.8	90.1
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 2.05	$ 1.11	$ 2.59	$ 3.24
Discontinued operations (in dollars per share)	0	(0.01)	0	(0.01)
Net income (in dollars per share)	$ 2.05	$ 1.10	$ 2.59	$ 3.23
Weighted average common shares outstanding (in shares)	88.9	90.4	89.0	90.4
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)	87.8	89.2	87.8	89.2
New Vehicle [Member]
TOTAL REVENUE	$ 2,748.4	$ 2,874.8	$ 7,291.6	$ 8,141.1
TOTAL COST OF SALES (excluding depreciation shown below)	2,581.2	2,755.9	6,908.4	7,774.8
TOTAL GROSS PROFIT	167.2	118.9	383.2	366.3
Used Vehicle [Member]
TOTAL REVENUE	1,516.9	1,402.9	4,090.1	4,121.9
TOTAL COST OF SALES (excluding depreciation shown below)	1,370.0	1,310.6	3,735.2	3,842.3
TOTAL GROSS PROFIT	146.9	92.3	354.9	279.6
Parts and Service [Member]
TOTAL REVENUE	852.8	902.6	2,419.0	2,680.8
TOTAL COST OF SALES (excluding depreciation shown below)	477.6	493.6	1,343.6	1,461.0
TOTAL GROSS PROFIT	375.2	409.0	1,075.4	1,219.8
Finance and Insurance, Net [Member]
TOTAL REVENUE	281.2	266.2	763.4	757.9
TOTAL GROSS PROFIT	281.2	266.2	763.4	757.9
Product and Service, Other [Member]
TOTAL REVENUE	5.6	14.7	40.8	85.1
TOTAL COST OF SALES (excluding depreciation shown below)	4.6	13.7	38.0	81.3
TOTAL GROSS PROFIT	$ 1.0	$ 1.0	$ 2.8	$ 3.8