Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Operations (Detail) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations after income taxes		$ 0	$ 184	$ (41)
Less: Net income from discontinued operations attributable to noncontrolling interests		0	63	124
Net income (loss) from discontinued operations		$ 0	$ 121	(165)
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales	$ 6,752			10,121
Cost of goods sold (exclusive of expenses below)	5,655			7,965
Selling, general administrative, and other expenses	164			214
Research and development	28			69
Provision for depreciation, depletion and amortization	593			772
Restructuring and other charges	102			981
Interest expense	28			25
Other (income) expenses, net	(75)			30
Income from discontinued operations before income taxes	257			65
Provision for income taxes	73			106
Income (loss) from discontinued operations after income taxes	184			(41)
Less: Net income from discontinued operations attributable to noncontrolling interests	63			124
Net income (loss) from discontinued operations	$ 121			$ (165)