Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Loss contingency accrual	$ 16,000,000
Other assets	2,211,000,000	$ 2,226,000,000
Liability for remediation and reclamation obligations	113,000,000	$ 118,000,000
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	$ 103,000,000