Acquisitions and Divestitures - Additional Information (Detail)			1 Months Ended							12 Months Ended
	Jan. 31, 2020 USD ($)	Nov. 01, 2016 USD ($)	Jul. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Feb. 28, 2019 USD ($)	Nov. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2009	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) HydroelectricPowerDevelopment
Business Disposition [Line Items]
Restructuring and other charges										$ 1,031,000,000	$ 527,000,000	$ 309,000,000
Payments for restructuring										118,000,000	102,000,000	73,000,000
Asset impairment										225,000,000	$ 18,000,000	40,000,000
Cash provided at separation to Parent Company		$ 1,072,000,000										247,000,000
Divesture of MRC [Member]
Business Disposition [Line Items]
Restructuring and other charges				$ 319,000,000						$ 319,000,000
Alcoa Joint Venture [Member]
Business Disposition [Line Items]
Ownership interest in joint venture									25.10%
Equity interest				0.00%
Alcoa Corporation [Member]
Business Disposition [Line Items]
Ownership interest in joint venture										25.10%
Contributions to MRC				$ 100,000,000
Alcoa Corporation [Member] | Divesture of MRC [Member]
Business Disposition [Line Items]
Write off of investment				161,000,000
Cash contribution to an equity method investment				100,000,000
Write off delinquent payables due, forgiven				59,000,000
Gain from write off of the fair value of debt guarantee				1,000,000
Alcoa Corporation [Member] | Cost of Goods Sold [Member]
Business Disposition [Line Items]
Write down of remaining inventories					$ 16,000,000					$ 16,000,000
Ma’aden [Member]
Business Disposition [Line Items]
Contributions to MRC				$ 100,000,000
Saudi Arabia [Member] | Ma'aden Joint Venture [Member]
Business Disposition [Line Items]
Ownership interest percentage transferred				25.10%
Saudi Arabia [Member] | Ma’aden [Member] | Maaden Alcoa Joint Venture [Member]
Business Disposition [Line Items]
Ownership interest in joint venture									74.90%	74.90%
Restructuring And Other Charges [Member] | Alcoa Corporation [Member]
Business Disposition [Line Items]
Asset impairment					80,000,000					$ 80,000,000
Severance costs excluding employee related cost					20,000,000
Contract termination costs					8,000,000					8,000,000
Restructuring And Other Charges [Member] | Alcoa Corporation [Member] | Selling, General Administrative, and Other Expenses [Member]
Business Disposition [Line Items]
Restructuring and other charges					$ 2,000,000					2,000,000
Gum Springs | Subsequent Event [Member]
Business Disposition [Line Items]
Sale transaction value of waste processing	$ 250,000,000
Net cash received	200,000,000
Escrow to be received for divestitures	$ 50,000,000
Avilés and La Coruña Aluminum Facilities [Member] | Aviles and La Coruna Smelters [Member] | Spain [Member]
Business Disposition [Line Items]
Restructuring and other charges										127,000,000
Charge for working capital commitment and write-off remaining net book value of plants assets										32,000,000
Avilés and La Coruña Aluminum Facilities [Member] | Aviles and La Coruna Smelters [Member] | Spain [Member] | PARTER Capital Group AG [Member]
Business Disposition [Line Items]
Charges related to curtailment, employee dismissal process, and divestiture			$ 253,000,000
Payments for restructuring										47,000,000
Remaining cash outflows for restructuring expected to be paid in quarterly installments through second quarter of 2021										68,000,000
Avilés and La Coruña Aluminum Facilities [Member] | Aviles and La Coruna Smelters [Member] | Spain [Member] | PARTER Capital Group AG [Member] | Maximum [Member]
Business Disposition [Line Items]
Financial contributions										$ 95,000,000
Yadkin [Member]
Business Disposition [Line Items]
Net cash received						$ 8,000,000	$ 8,000,000	$ 249,000,000
Income (loss) from divestitures before income tax												122,000,000
Income (loss) from divestitures after income tax												$ 122,000,000
Cash provided at separation to Parent Company													$ 243,000,000
Number of hydroelectric power developments | HydroelectricPowerDevelopment													4