Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions		1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Apr. 22, 2020 kt	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Employee	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) Employee	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 37	$ 370		$ 39	$ 483
Payments for restructuring						71		$ 118
Curtailment of certain pension benefits				38		2	38
Restructuring reserve balance			105			105		137	$ 47
Noncurrent portion of the reserve			1			1		13
2019 Restructuring Plan Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 1			2
Number of affected employees associated with employee termination and severance costs | Employee			260
Number of separated employees associated with employee termination and severance costs | Employee			225
Payments for restructuring			$ 9			22
Increase (reduction) in foreign currency			$ 1			$ (1)
Restructuring and related cost number of eliminated positions were not replaced | Employee			60
The Point Comfort alumina refinery {Member] | Texas [Member]
Restructuring Cost and Reserve [Line Items]
Number of affected employees associated with employee termination and severance costs | Employee						40
Number of separated employees associated with employee termination and severance costs | Employee						30
Payments for restructuring			$ 1			$ 2
Aviles and La Coruna Smelters [Member]
Restructuring Cost and Reserve [Line Items]
Payments for restructuring			12			24
Restructuring reserve balance			44			44		68
Alcoa Corporation [Member] | Cost of Goods Sold [Member]
Restructuring Cost and Reserve [Line Items]
Write down of remaining inventories					$ 15
Alcoa Corporation [Member] | Restructuring And Other Charges [Member]
Restructuring Cost and Reserve [Line Items]
Contract termination costs					8
Asset impairment					80
Severance costs excluding employee related cost				3
Employee related expenses excluding severance costs				2	15
Alcoa Corporation [Member] | Restructuring And Other Charges [Member] | Selling, General Administrative, and Other Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Miscellaneous charges					$ 2
PARTER Capital Group AG [Member]
Restructuring Cost and Reserve [Line Items]
Noncurrent portion of the reserve								12
Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			27
Curtailment of smelting capacity | kt	230
Curtailed Smelting Capacity | kt	49
Contract termination costs			$ 11
Number of affected employees associated with employee termination and severance costs | Employee			685
Number of separated employees associated with employee termination and severance costs | Employee			250
Payments for restructuring			$ 2
Severance and Exit Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			27			27
Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			11			13
Severance and Other Employee Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Payments for restructuring						28		19
Restructuring reserve balance			25			$ 25		35	$ 5
Severance and Other Employee Termination Costs [Member] | 2019 Restructuring Plan Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve balance								27
Severance and Other Employee Termination Costs [Member] | The Point Comfort alumina refinery {Member] | Texas [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve balance								$ 4
Severance and Other Employee Termination Costs [Member] | Intalco [Member] | Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 17
Exit Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				5			108
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 delinquent payables due, forgiven		$ 59
Closure Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				1			8
Other Items Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 7			$ 10