Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Pension and other postretirement benefits (L)
Total Other comprehensive income (loss)	$ (18)	$ (8)	$ (28)	$ (12)
Foreign currency translation
Other comprehensive (loss) income	(76)	36	(252)	53
Cash flow hedges (M)
Net change from periodic revaluations	(153)	241	(36)	54
Net amount reclassified to earnings	74	27	127	64
Total Accumulated other comprehensive loss	(3,737)		(3,737)		$ (3,645)
Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	9	66		62
Unrecognized net actuarial gain/loss and prior service cost/benefit	10	(18)	14	(18)
Tax benefit (expense)	(2)	8	(3)	8
Total Other comprehensive income (loss) before reclassifications, net of tax	8	(10)	11	(10)
Amortization of net actuarial gain/loss and prior service cost/benefit	5	26	11	30
Tax benefit (expense)		(6)		(6)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	5	20	11	24
Total Other comprehensive income (loss)	13	10	22	14
Balance at end of period	22	76	22	76
Foreign currency translation
Balance at beginning of period	(2,715)	(2,683)	(2,593)	(2,685)
Other comprehensive (loss) income	(60)	25	(182)	27
Balance at end of period	(2,775)	(2,658)	(2,775)	(2,658)
Cash flow hedges (M)
Balance at beginning of period	(922)	(1,038)	(1,052)	(916)
Net change from periodic revaluations	(153)	241	(36)	54
Tax (expense) benefit	31	(38)
Total Other comprehensive income (loss) before reclassifications, net of tax	(122)	203	(36)	54
Net amount reclassified to earnings	74	27	127	64
Tax expense	(14)	(4)	(23)	(14)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	60	23	104	50
Total Other comprehensive income (loss)	(62)	226	68	104
Balance at end of period	(984)	(812)	(984)	(812)
Total Accumulated other comprehensive loss	(3,737)	(3,394)	(3,737)	(3,394)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	75	33	132	94
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings				(20)
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	(1)	(3)	(1)	(2)
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (M)
Net amount reclassified to earnings		(3)	(4)	(8)
Non-controlling Interest [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	(14)	(5)	(15)	(5)
Unrecognized net actuarial gain/loss and prior service cost/benefit	7	(2)	7	(2)
Tax benefit (expense)	(2)		(2)
Total Other comprehensive income (loss) before reclassifications, net of tax	5	(2)	5	(2)
Amortization of net actuarial gain/loss and prior service cost/benefit			1
Total amount reclassified from Accumulated other comprehensive loss, net of tax			1
Total Other comprehensive income (loss)	5	(2)	6	(2)
Balance at end of period	(9)	(7)	(9)	(7)
Foreign currency translation
Balance at beginning of period	(1,037)	(1,025)	(983)	(1,040)
Other comprehensive (loss) income	(16)	11	(70)	26
Balance at end of period	(1,053)	(1,014)	(1,053)	(1,014)
Cash flow hedges (M)
Balance at beginning of period		1		1
Net amount reclassified to earnings	(1)		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	(1)		(1)
Total Other comprehensive income (loss)	(1)		(1)
Balance at end of period	(1)	1	(1)	1
Total Accumulated other comprehensive loss	(1,063)	$ (1,020)	(1,063)	$ (1,020)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	$ (1)		$ (1)