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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Acquisitions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Jul. 31, 2012 Store	May 31, 2012 Store	May 31, 2011 Store
Business Acquisition [Line Items]
Number of convenience stores acquired	10	87	23
Acquisition of goodwill			$ 9
Gas America Services Inc [Member]
Business Acquisition [Line Items]
Number of convenience stores acquired		87
Acquisition of goodwill		83
Number of undeveloped real estate parcels acquired for future development		2
Road Ranger Llc [Member]
Business Acquisition [Line Items]
Number of convenience stores acquired	10
Acquisition of goodwill	5