Business Segments - Additional Information (Detail)	Sep. 30, 2011 Entity
United States | Refineries
Segment Reporting Information [Line Items]
Number of production facilities intended to close	2
United States | Downstream operation
Segment Reporting Information [Line Items]
Number of production facilities in United States represented as discontinued operations	1
United Kingdom | Downstream operation
Segment Reporting Information [Line Items]
Number of production facilities intended to close	1