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Interim Financial Statements (Business and Basis of Presentation) (Details)	9 Months Ended
	Sep. 30, 2018 brand store franchises
Product Information [Line Items]
Owned and operated new vehicle franchises | franchises	329
Number of stores (approximate number for total locations)	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 (approximate number for total locations)	242
Collision Centers [Member]
Product Information [Line Items]
Number of stores (approximate number for total locations)	82

X

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	an_
Data Type:	xbrli:integerItemType
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X

- Definition

Represents the number of owned and operated new vehicle franchises.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
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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

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Namespace Prefix:	an_
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Period Type:	duration

X

- Definition

Represents the number of stores.

+ References

No definition available.

+ Details

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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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X

- Details

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X

- Details

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