Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Loss contingency accrual	$ 269,000,000	$ 5,300,000,000
Other Assets	2,350,000,000	2,310,000,000
Liability for remediation and reclamation obligations	145,000,000	126,000,000
Landfill in West Covina, California [Member]
Loss Contingencies [Line Items]
Liability for remediation and reclamation obligations	50,000,000
Third Party Bankruptcy Assignment [Member]
Loss Contingencies [Line Items]
Litigation-related contingent loss	22,000,000	22,000,000	$ 117,000,000
Decommissioning obligations included in accrued expenses	116,000,000	$ 114,000,000
Pending Litigation [Member] | Peregrino Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency accrual	0
Pending Litigation [Member] | Amount Of Tax Originally In Dispute [Member] | Peregrino Litigation [Member]
Loss Contingencies [Line Items]
Other Assets	$ 86,000,000