Financial Instruments And Fair Value Measurements (Summary Of Carrying Values And Fair Values Of Fixed Rate Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed rate debt	$ 1,778.1	$ 1,778.6
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed rate debt	$ 1,864.4	$ 1,862.2

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