Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 53

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

Business Combinations (Details) (USD $) In Millions, unless otherwise specified	Feb. 28, 2013	Dec. 31, 2012 Ralph's Auto Supply (B.C.) Ltd. [Member] store	Dec. 31, 2012 U-Pick-It [Member] store	Dec. 31, 2012 Freetown/Millis Used Auto Parts [Member] store
Business Acquisition [Line Items]
Number of Stores		4	2	2
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 23
Business Acquisition, Purchase Price Allocation, Goodwill Amount	18
Business Acquisition, Purchase Price Allocation, Goodwill, Expected Tax Deductible Amount	$ 17