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Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Parenthetical) (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Restructuring Cost and Reserve [Line Items]          
Other layoff cost including reclassification in pension cost     $ 142   $ 246
Restructuring and other charges $ 66 $ 209 460 $ 780  
Pension Costs [Member]          
Restructuring Cost and Reserve [Line Items]          
Other layoff cost including reclassification in pension cost       26  
Restructuring and other charges   $ 18 11 18  
Pension And Other Postretirement Benefits [Member]          
Restructuring Cost and Reserve [Line Items]          
Other layoff cost including reclassification in pension cost     28    
Asset Retirement Obligations [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges     45 95  
Environmental Remediation [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges     $ 29 $ 47