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Business Segment Information - Financial Segment Information (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Segment Reporting Information [Line Items]        
Write-down of the carrying value of Oil and Gas properties $ 5,721 $ 1,562 $ 18,757 $ 1,765
United States [Member]        
Segment Reporting Information [Line Items]        
Write-down of the carrying value of Oil and Gas properties 4,301 1,545 13,855 1,545
Canada [Member]        
Segment Reporting Information [Line Items]        
Write-down of the carrying value of Oil and Gas properties 973   3,160  
North Sea [Member]        
Segment Reporting Information [Line Items]        
Write-down of the carrying value of Oil and Gas properties $ 447 17 $ 1,742 220
Australia [Member]        
Segment Reporting Information [Line Items]        
Total Assets   $ 8,700   $ 8,700