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v3.8.0.1

Acquisitions (Details) - store | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Collision Centers [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of stores purchased | 7 | 1 |
Dealerships [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of stores purchased | 1 | 20 | 22

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

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- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
Name: | us-gaap_NumberOfBusinessesAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

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