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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

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