Properties, Plants, and Equipment, Net - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Jul. 31, 2017 kt	Dec. 31, 2017 USD ($) kt	Dec. 31, 2016 USD ($) kt
Property, Plant and Equipment [Line Items]
Refining capacity closed		191
Refining ideal capacity closed		778
Partially started smelter capacity	161
Carrying value of the smelter and related assets | $		$ 17,447,000,000	$ 16,741,000,000
Smelting Assets [Member]
Property, Plant and Equipment [Line Items]
Net carrying value of assets | $		$ 248,000,000	$ 314,000,000
Idle capacity of assets, units	269	856	778
Idled Refining Assets [Member]
Property, Plant and Equipment [Line Items]
Net carrying value of assets | $		$ 141,000,000	$ 158,000,000
Idle capacity of assets, units		2,305	2,305
Smelting and Related Assets [Member]
Property, Plant and Equipment [Line Items]
Carrying value of the smelter and related assets | $		$ 0