Financial Instruments and Fair Value Measurements (Summary Of Carrying Values And Fair Values Of Fixed Rate Debt) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed rate debt	$ 997.3	$ 652.0
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed rate debt	$ 1,086.2	$ 675.6

The total amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a fixed rate. This element is used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

No definition available.

Name:	an_FixedRateDebtFairValue
Namespace Prefix:	an_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant