Unaudited Condensed Consolidated Income Statements - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
TOTAL REVENUE		$ 5,432.4	$ 5,567.5	$ 15,851.1	$ 16,128.5
TOTAL COST OF SALES (excluding depreciation shown below)		4,586.5	4,731.1	13,359.3	13,624.4
TOTAL GROSS PROFIT		845.9	836.4	2,491.8	2,504.1
Selling, general, and administrative expenses		607.5	591.3	1,814.1	1,765.2
Depreciation and amortization		41.4	36.3	118.0	107.0
Other income, net		(14.2)	(10.2)	(54.4)	(21.0)
OPERATING INCOME		211.2	219.0	614.1	652.9
Non-operating income (expense) items:
Floorplan interest expense		(25.1)	(18.2)	(70.7)	(56.4)
Other interest expense		(30.0)	(28.9)	(88.0)	(85.9)
Interest income		0.2	0.3	0.8	0.8
Other income, net		1.6	2.6	6.4	3.4
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		157.9	174.8	462.6	514.8
Income tax provision		60.3	67.0	179.1	198.7
NET INCOME FROM CONTINUING OPERATIONS		97.6	107.8	283.5	316.1
Loss from discontinued operations, net of income taxes		(0.1)	(0.5)	(0.2)	(0.9)
NET INCOME		$ 97.5	$ 107.3	$ 283.3	$ 315.2
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	[1]	$ 1.00	$ 1.06	$ 2.84	$ 3.05
Discontinued operations (in dollars per share)	[1]	0.00	0.00	0.00	(0.01)
Net income (in dollars per share)	[1]	$ 1.00	$ 1.05	$ 2.84	$ 3.04
Weighted average common shares outstanding (in shares)		97.3	101.9	99.9	103.8
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	[1]	$ 1.00	$ 1.05	$ 2.83	$ 3.02
Discontinued operations (in dollars per share)	[1]	0.00	0.00	0.00	(0.01)
Net income (in dollars per share)	[1]	$ 1.00	$ 1.05	$ 2.82	$ 3.02
Weighted average common shares outstanding (in shares)		97.7	102.6	100.3	104.5
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)		91.2	101.2	91.2	101.2
New Vehicle [Member]
TOTAL REVENUE		$ 3,108.4	$ 3,195.9	$ 8,835.5	$ 9,068.0
TOTAL COST OF SALES (excluding depreciation shown below)		2,963.6	3,037.7	8,408.2	8,597.8
TOTAL GROSS PROFIT		144.8	158.2	427.3	470.2
Used Vehicle [Member]
TOTAL REVENUE		1,228.3	1,276.8	3,670.3	3,777.8
TOTAL COST OF SALES (excluding depreciation shown below)		1,142.6	1,199.6	3,433.1	3,525.6
TOTAL GROSS PROFIT		85.7	77.2	237.2	252.2
Parts and Service [Member]
TOTAL REVENUE		841.6	843.8	2,544.2	2,498.9
TOTAL COST OF SALES (excluding depreciation shown below)		474.2	480.0	1,428.2	1,418.8
TOTAL GROSS PROFIT		367.4	363.8	1,116.0	1,080.1
Finance and Insurance, Net [Member]
TOTAL REVENUE		241.6	229.6	692.0	678.1
TOTAL GROSS PROFIT		241.6	229.6	692.0	678.1
Other Goods and Services [Member]
TOTAL REVENUE		12.5	21.4	109.1	105.7
TOTAL COST OF SALES (excluding depreciation shown below)		6.1	13.8	89.8	82.2
TOTAL GROSS PROFIT		$ 6.4	$ 7.6	$ 19.3	$ 23.5

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