Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Cash Flows (Detail) - Alcoa Corporation [Member] $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation, depletion and amortization	$ 532
Restructuring and other charges	101
Capital expenditures	$ 258