Consolidated Income Statements (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
TOTAL REVENUE		$ 19,108.8us-gaap_Revenues	$ 17,517.6us-gaap_Revenues	$ 15,667.5us-gaap_Revenues
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)		16,120.1us-gaap_CostOfRevenue	14,757.7us-gaap_CostOfRevenue	13,181.3us-gaap_CostOfRevenue
Gross Profit:
TOTAL GROSS PROFIT		2,988.7us-gaap_GrossProfit	2,759.9us-gaap_GrossProfit	2,486.2us-gaap_GrossProfit
Selling, general, and administrative expenses		2,079.6	1,935.0	1,749.3
Depreciation and amortization		106.9	95.3	87.3
Franchise rights impairment		0	0	4.2
Other expenses (income), net		(18.6)us-gaap_OtherOperatingIncomeExpenseNet	(10.7)us-gaap_OtherOperatingIncomeExpenseNet	0.1us-gaap_OtherOperatingIncomeExpenseNet
OPERATING INCOME		820.8us-gaap_OperatingIncomeLoss	740.3us-gaap_OperatingIncomeLoss	645.3us-gaap_OperatingIncomeLoss
Non-operating income (expense) items:
Floorplan interest expense		(53.3)an_FloorplanInterestExpense	(53.4)an_FloorplanInterestExpense	(45.5)an_FloorplanInterestExpense
Other interest expense		(86.7)us-gaap_InterestExpenseDebt	(88.3)us-gaap_InterestExpenseDebt	(86.9)us-gaap_InterestExpenseDebt
Loss on debt extinguishment	(1.6)	(1.6)	0	0
Interest income		0.2us-gaap_InvestmentIncomeInterest	0.2us-gaap_InvestmentIncomeInterest	0.3us-gaap_InvestmentIncomeInterest
Other income, net		2.9us-gaap_OtherNonoperatingIncomeExpense	5.6us-gaap_OtherNonoperatingIncomeExpense	3.6us-gaap_OtherNonoperatingIncomeExpense
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		682.3	604.4	516.8
Income tax provision		262.5us-gaap_IncomeTaxExpenseBenefit	228.6us-gaap_IncomeTaxExpenseBenefit	199.5us-gaap_IncomeTaxExpenseBenefit
NET INCOME FROM CONTINUING OPERATIONS		419.8	375.8	317.3
Loss from discontinued operations, net of income taxes		(1.1)	(0.9)	(0.9)
NET INCOME		418.7us-gaap_NetIncomeLoss	374.9us-gaap_NetIncomeLoss	316.4us-gaap_NetIncomeLoss
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)		$ 3.58	$ 3.10	$ 2.56
Discontinued operations (in dollars per share)		$ (0.01)	$ (0.01)	$ (0.01)
Net income (in dollars per share)		$ 3.57us-gaap_EarningsPerShareBasic	$ 3.09us-gaap_EarningsPerShareBasic	$ 2.56us-gaap_EarningsPerShareBasic
Weighted average common shares outstanding (in shares)		117.3	121.3	123.8
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)		$ 3.53	$ 3.05	$ 2.52
Discontinued operations (in dollars per share)		$ (0.01)	$ (0.01)	$ (0.01)
Net income (in dollars per share)		$ 3.52us-gaap_EarningsPerShareDiluted	$ 3.04us-gaap_EarningsPerShareDiluted	$ 2.52us-gaap_EarningsPerShareDiluted
Weighted average common shares outstanding (in shares)		118.9	123.3	125.8
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)	113.3us-gaap_CommonStockSharesOutstanding	113.3us-gaap_CommonStockSharesOutstanding	120.9us-gaap_CommonStockSharesOutstanding	120.9us-gaap_CommonStockSharesOutstanding
New Vehicle [Member]
Revenue:
TOTAL REVENUE		10,972.2	9,949.6	8,906.2
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)		10,322.1	9,333.2	8,326.7
Gross Profit:
TOTAL GROSS PROFIT		650.1	616.4	579.5
Used Vehicle [Member]
Revenue:
TOTAL REVENUE		4,385.7	4,127.4	3,714.3
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)		4,025.1	3,797.7	3,415.1
Gross Profit:
TOTAL GROSS PROFIT		360.6	329.7	299.2
Parts and Service [Member]
Revenue:
TOTAL REVENUE		2,822.5	2,597.4	2,399.2
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)		1,625.9	1,491.6	1,391.2
Gross Profit:
TOTAL GROSS PROFIT		1,196.6	1,105.8	1,008.0
Finance and Insurance, Net [Member]
Revenue:
TOTAL REVENUE		750.8	674.0	571.2
Gross Profit:
TOTAL GROSS PROFIT		750.8	674.0	571.2
Other Goods and Services [Member]
Revenue:
TOTAL REVENUE		177.6	169.2	76.6
Cost of Sales:
TOTAL COST OF SALES (excluding depreciation shown below)		147.0	135.2	48.3
Gross Profit:
TOTAL GROSS PROFIT		$ 30.6	$ 34.0	$ 28.3

The aggregate expense recognized in the current period that reflects the allocation of the cost of tangible assets and intangible assets over the assets' useful lives. This concept does not include the amortization of debt financing costs and discounts.

No definition available.