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Financial Instruments And Fair Value Measurements (Summary Of Carrying Values And Fair Values Of Fixed Rate Debt) (Details) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Reported Value Measurement [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed rate debt | $ 1,781.2 | $ 1,778.6
Fair Value [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed rate debt | $ 1,858.4 | $ 1,862.2

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- Definition 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. + References No definition available. + Details
Name: | an_FixedRateDebtFairValue
Namespace Prefix: | an_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |