Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Operations (Details) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations after income taxes		$ 0	$ 0	$ 184
Less: Net income from discontinued operations attributable to noncontrolling interests		0	0	63
Net income from discontinued operations		$ 0	$ 0	$ 121
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales	$ 6,752
Cost of goods sold (exclusive of expenses below)	5,655
Selling, general administrative, and other expenses	164
Research and development	28
Provision for depreciation, depletion and amortization	593
Restructuring and other charges	102
Interest expense	28
Other (income) expenses, net	(75)
Income from discontinued operations before income taxes	257
Provision for income taxes	73
Income from discontinued operations after income taxes	184
Less: Net income from discontinued operations attributable to noncontrolling interests	63
Net income from discontinued operations	$ 121