Unaudited Condensed Consolidated Income Statements - USD ($) shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Document Fiscal Year Focus				2020
TOTAL REVENUE		$ 4,533.0	$ 5,343.8	$ 9,200.0	$ 10,325.6
TOTAL COST OF SALES (excluding depreciation shown below)		3,738.0	4,453.0	7,591.8	8,585.6
TOTAL GROSS PROFIT		795.0	890.8	1,608.2	1,740.0
Selling, general, and administrative expenses		547.9	637.0	1,148.6	1,260.0
Depreciation and amortization		49.1	44.4	97.2	88.5
Goodwill impairment		0.0	0.0	318.3	0.0
Franchise rights impairment		0.0	9.6	57.5	9.6
Other (income) expense, net		(3.4)	(3.7)	4.5	(12.4)
OPERATING INCOME (LOSS)		201.4	203.5	(17.9)	394.3
Non-operating income (expense) items:
Floorplan interest expense		(16.3)	(37.4)	(41.8)	(76.4)
Other interest expense		(23.2)	(27.7)	(46.7)	(55.5)
Interest income		0.1	0.1	0.2	0.3
Other income (loss), net		214.5	(0.3)	211.5	1.6
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		376.5	138.2	105.3	264.3
Income tax provision		96.6	37.2	57.6	71.2
NET INCOME FROM CONTINUING OPERATIONS		279.9	101.0	47.7	193.1
Loss from discontinued operations, net of income taxes		(0.1)	(0.2)	(0.2)	(0.3)
NET INCOME		$ 279.8	$ 100.8	$ 47.5	$ 192.8
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	[1]	$ 3.18	$ 1.12	$ 0.54	$ 2.14
Discontinued operations (in dollars per share)	[1]	0	0	0	0
Net income (in dollars per share)	[1]	$ 3.18	$ 1.12	$ 0.53	$ 2.14
Weighted average common shares outstanding (in shares)		87.9	89.9	89.0	90.2
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	[1]	$ 3.18	$ 1.12	$ 0.54	$ 2.14
Discontinued operations (in dollars per share)	[1]	0	0	0	0
Net income (in dollars per share)	[1]	$ 3.18	$ 1.12	$ 0.53	$ 2.13
Weighted average common shares outstanding (in shares)		88.1	90.2	89.0	90.4
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)		87.2	89.1	87.2	89.1
New Vehicle [Member]
TOTAL REVENUE		$ 2,261.3	$ 2,769.6	$ 4,543.2	$ 5,266.3
TOTAL COST OF SALES (excluding depreciation shown below)		2,141.7	2,644.1	4,327.2	5,018.9
TOTAL GROSS PROFIT		119.6	125.5	216.0	247.4
Used Vehicle [Member]
TOTAL REVENUE		1,324.5	1,379.4	2,573.2	2,719.0
TOTAL COST OF SALES (excluding depreciation shown below)		1,207.5	1,282.6	2,365.2	2,531.7
TOTAL GROSS PROFIT		117.0	96.8	208.0	187.3
Parts and Service [Member]
TOTAL REVENUE		689.9	901.5	1,566.2	1,778.2
TOTAL COST OF SALES (excluding depreciation shown below)		378.5	489.6	866.0	967.4
TOTAL GROSS PROFIT		311.4	411.9	700.2	810.8
Finance and Insurance, Net [Member]
TOTAL REVENUE		246.4	255.2	482.2	491.7
TOTAL GROSS PROFIT		246.4	255.2	482.2	491.7
Product and Service, Other [Member]
TOTAL REVENUE		10.9	38.1	35.2	70.4
TOTAL COST OF SALES (excluding depreciation shown below)		10.3	36.7	33.4	67.6
TOTAL GROSS PROFIT		$ 0.6	$ 1.4	$ 1.8	$ 2.8

[1] Earnings per share amounts are calculated discretely and therefore may not add up to the total due to rounding.