Basis of Presentation - Schedule of Cost Allocation (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basis Of Presentation [Line Items]
Cost of goods sold			$ 9,072	$ 7,898	$ 9,039
Selling, general administrative, and other expenses			284	359	353
Research and development expenses			32	33	69
Provision for depreciation, depletion, and amortization			750	718	780
Restructuring and other charges	$ 297	$ 209	309	318	983
Interest expense			104	243	270
Other (income) expenses, net			$ 58	89	(42)
Alcoa Corporation [Member]
Basis Of Presentation [Line Items]
Cost of goods sold				40	93
Selling, general administrative, and other expenses				150	146
Research and development expenses				2	17
Provision for depreciation, depletion, and amortization				18	22
Restructuring and other charges				1	32
Interest expense				198	245
Other (income) expenses, net				$ (7)	$ 12