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Business And Credit Concentrations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Percentage of new vehicle sales from core brands	95.00%an_PercentageOfNewVehicleSalesCoreBrands
Manufacturer receivables	$ 180.4an_ManufacturerReceivables	$ 198.3an_ManufacturerReceivables

X

- Definition

The amount due to the company from manufacturers or distributors, within one year of the balance sheet date, including (1) rebates and assistance for holdbacks, floorplan interest and advertising expenses; (2) incentives based on achieving certain objectives; and (3) amounts due for warranty and service work performed for customers.

+ References

No definition available.

+ Details

Name:	an_ManufacturerReceivables
Namespace Prefix:	an_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The percentage of new vehicles sold that represent the core brands of new vehicles sold by the company.

+ References

No definition available.

+ Details

Name:	an_PercentageOfNewVehicleSalesCoreBrands
Namespace Prefix:	an_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RisksAndUncertaintiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration