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Acquisitions (Details) - stores	1 Months Ended		9 Months Ended
	Oct. 31, 2015	Aug. 31, 2015	Sep. 30, 2015	Sep. 30, 2014
Subsequent Event [Line Items]
Number of stores purchased			8	1
Number of stores announced to be acquired		13
Acquisition Announcement [Member]
Subsequent Event [Line Items]
Number of stores announced to be acquired	12

X

- Definition

The number of stores that the company has announced will be acquired in a future period.

+ References

No definition available.

+ Details

Name:	an_NumberOfStoresAnnouncedToBeAcquired
Namespace Prefix:	an_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- 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

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_SubsequentEventTypeAxis=an_AcquisitionAnnouncementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: