Consolidated Statements of Income - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
TOTAL REVENUE	$ 25,844,000,000	$ 20,390,000,000	$ 21,335,700,000
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)	20,891,400,000	16,823,600,000	17,812,700,000
Gross Profit:
TOTAL GROSS PROFIT	4,952,600,000	3,566,400,000	3,523,000,000
Selling, general, and administrative expenses	2,876,200,000	2,422,000,000	2,558,600,000
Depreciation and amortization	193,300,000	198,900,000	180,500,000
Goodwill impairment	0	318,300,000	0
Franchise rights impairment	0	57,500,000	9,600,000
Other (income) expense, net	(19,700,000)	6,500,000	(49,300,000)
OPERATING INCOME	1,902,800,000	563,200,000	823,600,000
Non-operating income (expense) items:
Floorplan interest expense	(25,700,000)	(63,800,000)	(138,400,000)
Other interest expense	(93,000,000.0)	(93,700,000)	(106,700,000)
Other income, net	24,300,000	144,400,000	34,100,000
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,808,400,000	550,100,000	612,600,000
Income tax provision	435,100,000	168,300,000	161,800,000
NET INCOME FROM CONTINUING OPERATIONS	1,373,300,000	381,800,000	450,800,000
Loss from discontinued operations, net of income taxes	(300,000)	(200,000)	(800,000)
Net income	$ 1,373,000,000	$ 381,600,000	$ 450,000,000.0
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 18.51	$ 4.32	$ 5.00
Discontinued operations (in dollars per share)	0	0	(0.01)
Net income (in dollars per share)	$ 18.50	$ 4.32	$ 4.99
Weighted average common shares outstanding, basic (in shares)	74.2	88.3	90.1
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 18.31	$ 4.30	$ 4.98
Discontinued operations (in dollars per share)	0	0	(0.01)
Net income (in dollars per share)	$ 18.31	$ 4.30	$ 4.97
Weighted average common shares outstanding (in shares)	75.0	88.7	90.5
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)	62.6	83.5	89.3
New Vehicle [Member]
Revenue:
TOTAL REVENUE	$ 12,081,700,000	$ 10,418,600,000	$ 11,166,500,000
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)	10,880,100,000	9,834,500,000	10,662,600,000
Gross Profit:
TOTAL GROSS PROFIT	1,201,600,000	584,100,000	503,900,000
Used Vehicle [Member]
Revenue:
TOTAL REVENUE	8,638,800,000	5,601,300,000	5,466,500,000
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)	7,950,700,000	5,142,300,000	5,098,500,000
Gross Profit:
TOTAL GROSS PROFIT	688,100,000	459,000,000.0	368,000,000.0
Parts and Service [Member]
Revenue:
TOTAL REVENUE	3,706,600,000	3,257,400,000	3,572,100,000
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)	2,033,900,000	1,796,600,000	1,949,500,000
Gross Profit:
TOTAL GROSS PROFIT	1,672,700,000	1,460,800,000	1,622,600,000
Finance and Insurance, Net [Member]
Revenue:
TOTAL REVENUE	1,384,500,000	1,059,300,000	1,023,300,000
Gross Profit:
TOTAL GROSS PROFIT	1,384,500,000	1,059,300,000	1,023,300,000
Product and Service, Other [Member]
Revenue:
TOTAL REVENUE	32,400,000	53,400,000	107,300,000
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)	26,700,000	50,200,000	102,100,000
Gross Profit:
TOTAL GROSS PROFIT	$ 5,700,000	$ 3,200,000	$ 5,200,000