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Interim Financial Statements (Business and Basis of Presentation) (Details) | 6 Months Ended
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Jun. 30, 2018 brand store franchises
Product Information [Line Items] |
Owned and operated new vehicle franchises | franchises | 331
Number of stores | 325
Number of brands | brand | 33
Percentage of new vehicle sales from core brands (percent) | 93.00%
Dealerships [Member] |
Product Information [Line Items] |
Number of stores | 242
Collision Centers [Member] |
Product Information [Line Items] |
Number of stores | 80

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
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ConsolidatedEntitiesAxis=an_DealershipsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConsolidatedEntitiesAxis=an_CollisionCentersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |