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Description of Business and Summary of Significant Accounting Policies (Organization and Business, Inventory) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 brand franchises stores	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Owned and operated new vehicle franchises	276an_OwnedAndOperatedNewVehicleFranchises
Number of stores	232us-gaap_NumberOfStores
Number of brands	34an_NumberOfBrands
Percentage of new vehicle sales core brand vehicles	95.00%an_PercentageOfNewVehicleSalesCoreBrands
Floorplan interest assistance, inventory cost reduction	$ 17.9an_FloorplanAssistanceInventoryCostReduction	$ 19.7an_FloorplanAssistanceInventoryCostReduction

X

- Definition

The amount of floorplan assistance received from manufacturers for new vehicles in inventory as of period-end. The amount is reflected as a reduction to new vehicle inventory cost.

+ References

No definition available.

+ Details

Name:	an_FloorplanAssistanceInventoryCostReduction
Namespace Prefix:	an_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The number of new vehicle brands sold by the company's stores.

+ References

No definition available.

+ Details

Name:	an_NumberOfBrands
Namespace Prefix:	an_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Represents the number of owned and operated new vehicle franchises.

+ References

No definition available.

+ Details

Name:	an_OwnedAndOperatedNewVehicleFranchises
Namespace Prefix:	an_
Data Type:	xbrli:integerItemType
Balance Type:	na
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

- Definition

Represents the number of stores.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStores
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

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