Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended
	Feb. 28, 2019 Location kt	Dec. 31, 2009	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 27, 2019 USD ($)	Dec. 31, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 370		$ 231	$ 483	$ 212
Curtailments related to retirement benefits			38			38
Number of locations, curtailed the smelters as per dismissal process | Location	2
Combined operating capacity | kt	124
Curtailment of certain pension and other postretirement employee benefits					167		144
Noncurrent portion of the reserve			$ 2			$ 2
Maaden Alcoa Joint Venture [Member]
Restructuring Cost and Reserve [Line Items]
Non-controlling interest, ownership percentage		25.10%	25.10%			25.10%
Maaden Alcoa Joint Venture [Member]
Restructuring Cost and Reserve [Line Items]
Equity investments			$ 638			$ 638			$ 874
Ma'aden Joint Venture [Member] | Saudi Arabia [Member]
Restructuring Cost and Reserve [Line Items]
Ownership interest percentage transferred			25.10%			25.10%
Alcoa Joint Venture [Member]
Restructuring Cost and Reserve [Line Items]
Equity interest			0.00%
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Project financing Investment								$ 296
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Contributions to MRC			$ 100
Ma’aden [Member] | Maaden Alcoa Joint Venture [Member] | Saudi Arabia [Member]
Restructuring Cost and Reserve [Line Items]
Ownership interest in joint venture		74.90%	74.90%			74.90%
Ma'aden Joint Venture [Member]
Restructuring Cost and Reserve [Line Items]
Contributions to MRC			$ 100
Ma'aden Joint Venture [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Project financing Investment			296			$ 296
Maaden Alcoa Joint Venture [Member]
Restructuring Cost and Reserve [Line Items]
Write off of MRC delinquent payables			235
Cost of Goods Sold [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Write down of remaining inventories				$ 15
Restructuring And Other Charges [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Asset impairment				80
Contract termination costs				8
Severance costs excluding employee related cost			3
Employee related expenses excluding severance costs			2	15
Restructuring And Other Charges [Member] | Selling, General Administrative, and Other Expenses [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 2
Exit Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			5			108
Closure Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			1			8
Divesture of MRC [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			319			319
Divesture of MRC [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Write off of investment						161
Cash contribution to an equity method investment						100
Gain from write off of the fair value of debt guarantee						1
Write off delinduent payables due, forgiven						59
Miscellaneous Items Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 7			$ 10
Net benefit					1		1
Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					80		84
Net benefit					$ 15		$ 15