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Contingencies and Commitments - Accrued Liabilities for Remediation Activities Included in Balance Sheet (Detail) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Loss Contingencies [Line Items]    
Total $ 179 $ 179
Accounts payable    
Loss Contingencies [Line Items]    
Total 29 29
Deferred credits and other noncurrent liabilities    
Loss Contingencies [Line Items]    
Total $ 150 $ 150