LONG-TERM DEBT (Schedule of Mortgage Notes Payable) (Details) - Mortgages [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Aggregate Principal Outstanding	$ 356.2	$ 303.8
Carrying Value of Collateralized Related Real Estate	553.2	477.1
Captive Mortgage [Member]
Debt Instrument [Line Items]
Aggregate Principal Outstanding	170.3	190.5
Carrying Value of Collateralized Related Real Estate	241.1	265.7
Other Mortgage Debt [Member]
Debt Instrument [Line Items]
Aggregate Principal Outstanding	24.0	24.6
Carrying Value of Collateralized Related Real Estate	45.7	38.1
Real Estate Credit Agreement [Member]
Debt Instrument [Line Items]
Aggregate Principal Outstanding	64.0	71.5
Carrying Value of Collateralized Related Real Estate	131.7	140.0
Restated Master Loan Agreement [Member]
Debt Instrument [Line Items]
Aggregate Principal Outstanding	97.9	17.2
Carrying Value of Collateralized Related Real Estate	$ 134.7	$ 33.3

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.

No definition available.

+ Details

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

- Definition

Total carrying amount of mortgage loans as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.6)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

Name:	us-gaap_MortgageLoansOnRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount, as of the date of the latest financial statement presented, of real estate owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

Name:	us-gaap_PledgedAssetsNotSeparatelyReportedRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abg_MortgageAgreementAxis=abg_CaptiveMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abg_MortgageAgreementAxis=abg_OtherMortgageDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abg_MortgageAgreementAxis=abg_RealEstateCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abg_MortgageAgreementAxis=abg_MasterLoanAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: