Unaudited Condensed Consolidated Income Statements (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
TOTAL REVENUE	$ 4,944.2us-gaap_Revenues	$ 4,363.5us-gaap_Revenues
TOTAL COST OF SALES (excluding depreciation shown below)	4,144.3us-gaap_CostOfRevenue	3,656.1us-gaap_CostOfRevenue
TOTAL GROSS PROFIT	799.9us-gaap_GrossProfit	707.4us-gaap_GrossProfit
Selling, general, and administrative expenses	557.6	500.7
Depreciation and amortization	28.7	25.6
Other income, net	(1.3)us-gaap_OtherOperatingIncomeExpenseNet	(8.0)us-gaap_OtherOperatingIncomeExpenseNet
OPERATING INCOME	214.9us-gaap_OperatingIncomeLoss	189.1us-gaap_OperatingIncomeLoss
Non-operating income (expense) items:
Floorplan interest expense	(13.2)an_FloorplanInterestExpense	(13.2)an_FloorplanInterestExpense
Other interest expense	(21.4)us-gaap_InterestExpenseDebt	(21.6)us-gaap_InterestExpenseDebt
Interest income	0.1us-gaap_InvestmentIncomeInterest	0us-gaap_InvestmentIncomeInterest
Other income, net	1.1us-gaap_OtherNonoperatingIncomeExpense	1.5us-gaap_OtherNonoperatingIncomeExpense
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	181.5	155.8
Income tax provision	69.8us-gaap_IncomeTaxExpenseBenefit	60.3us-gaap_IncomeTaxExpenseBenefit
NET INCOME FROM CONTINUING OPERATIONS	111.7	95.5
Loss from discontinued operations, net of income taxes	(0.2)	(0.4)
NET INCOME	111.5us-gaap_NetIncomeLoss	95.1us-gaap_NetIncomeLoss
BASIC EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 0.98	$ 0.80
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00
Net income (in dollars per share)	$ 0.98us-gaap_EarningsPerShareBasic	$ 0.80us-gaap_EarningsPerShareBasic
Weighted average common shares outstanding (in shares)	113.6	119.5
DILUTED EARNINGS (LOSS) PER SHARE:
Continuing operations (in dollars per share)	$ 0.97	$ 0.79
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00
Net income (in dollars per share)	$ 0.97us-gaap_EarningsPerShareDiluted	$ 0.78us-gaap_EarningsPerShareDiluted
Weighted average common shares outstanding (in shares)	115.1	121.3
COMMON SHARES OUTSTANDING, net of treasury stock, at period end (in shares)	113.9us-gaap_CommonStockSharesOutstanding	119.4us-gaap_CommonStockSharesOutstanding
New Vehicle [Member]
TOTAL REVENUE	2,769.6	2,428.6
TOTAL COST OF SALES (excluding depreciation shown below)	2,608.1	2,282.7
TOTAL GROSS PROFIT	161.5	145.9
Used Vehicle [Member]
TOTAL REVENUE	1,193.2	1,049.7
TOTAL COST OF SALES (excluding depreciation shown below)	1,089.5	955.4
TOTAL GROSS PROFIT	103.7	94.3
Parts and Service [Member]
TOTAL REVENUE	743.4	671.0
TOTAL COST OF SALES (excluding depreciation shown below)	423.4	384.3
TOTAL GROSS PROFIT	320.0	286.7
Finance and Insurance, Net [Member]
TOTAL REVENUE	207.6	172.4
TOTAL GROSS PROFIT	207.6	172.4
Other Goods and Services [Member]
TOTAL REVENUE	30.4	41.8
TOTAL COST OF SALES (excluding depreciation shown below)	23.3	33.7
TOTAL GROSS PROFIT	$ 7.1	$ 8.1

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.