Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2019 Smelter kt	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019	Jun. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 113	$ (19)
Number of smelters | Smelter	2
Combined operating capacity | kt	124
Net gain related to curtailment of certain pension and other postretirement employee benefits			23
Noncurrent portion of the reserve		11
Noncurrent portion of reserve expected to be paid in 2020		8
Scenario Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring-related charges cash percentage				75.00%
Scenario Forecast [Member] | Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 70
Restructuring charges, after-tax					70
Scenario Forecast [Member] | Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					125
Restructuring charges, after-tax					$ 125
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
Employee-related cost		15
Restructuring And Other Charges [Member] | Selling, General Administrative, and Other Expenses [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Miscellaneous charges		2
Exit Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		103
Closure Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		7
Miscellaneous Items Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 3
Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 4