Commitments and Contingencies - Environmental (Details) (Laurel, Montana and McPherson, Kansas Refineries [Member], USD $) In Millions, unless otherwise specified	12 Months Ended	48 Months Ended
Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2012
Laurel, Montana and McPherson, Kansas Refineries [Member]
Site Contingency [Line Items]
Payments for Environmental Liabilities			$ 95.0
Environmental Remediation Expense	$ 19.0	$ 43.0

Cash outflows made during the period for environmental remediation activities.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 17

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3367-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration