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Asset Retirement Obligations and Accrued Environmental Costs - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Accrued environmental costs $ 922 $ 994
Maximum number of years accrued environmental liabilities will be paid over 30 years  
Expected expenditures for acquired environmental obligations, weighted-average discount factor rate 5.00%  
Present value of the estimated aggregate accrual for environmental loss contingencies 427  
Accrued environmental costs, undiscounted due within one year 58  
Accrued environmental costs, undiscounted due within second year 44  
Accrued environmental costs, undiscounted due within three year 22  
Accrued environmental costs, undiscounted due within fourth year 19  
Accrued environmental costs, undiscounted due within fifth year 20  
Accrued environmental costs, undiscounted due after fifth year 373  
Cleanup, Remediation Activities [Member]
    
Accrued environmental costs 571 624
Corporate and Other Environmental Liabilities [Member]
    
Accrued environmental costs 274 278
Federal Comprehensive Environmental Response Compensation and Liability Act, or Similar State Laws [Member]
    
Accrued environmental costs $ 77 $ 92