The date of the annual goodwill and indefinite-lived franchise rights impairment test.

No definition available.

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Period Type:	duration

- Definition

The amount of impairment loss recognized in the period, resulting from the write-down of the carrying amount of an indefinite-lived intangible asset, other than goodwill, to fair value, net of taxes.

+ References

No definition available.

+ Details

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Namespace Prefix:	an_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of an indefinite-lived intangible asset, other than goodwill, to fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16373-109275

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 46

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount (original costs adjusted for previously recognized amortization and impairment) as of the balance sheet date for the rights acquired through a franchise arrangement having an indefinite period of benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

+ Details

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Period Type:	instant

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Period Type:	duration

Goodwill and Intangible Assets (Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights impairment	$ 4.2	$ 0	$ 0
Franchise rights - indefinite-lived	285.7	212.6
Franchise rights [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Date of Annual Goodwill and Indefinite Lived Intangible Assets Impairment Test	April 30	April 30	April 30
Nonrecurring [Member] \| Franchise rights [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights impairment	4.2	0	0
Franchise rights impairment, after tax	2.6
Operating Segments, Domestic [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	22.8
Operating Segments, Import [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	78.9
Operating Segments, Premium Luxury [Member]
Indefinite-lived Intangible Assets by Segment [Line Items]
Franchise rights - indefinite-lived	$ 184.0