Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension and other postretirement benefits (O)
Total Other comprehensive (loss) income	$ (4)	$ 72	$ (952)
Acquisition of noncontrolling interest (C)	(193)
Foreign currency translation
Other comprehensive (loss) income	(618)	149	(174)
Cash flow hedges (P)
Net change from periodic revaluations	(93)	(295)
Net amount reclassified to earnings	288	130
Total Accumulated other comprehensive loss	(5,110)	(3,645)
Alcoa Corporation [Member]
Pension and other postretirement benefits (O)
Balance at beginning of period		62	(882)
Unrecognized net actuarial gain/loss and prior service cost/benefit	(17)	(112)	263
Tax (expense) benefit	(4)	17	(42)
Total Other comprehensive (loss) income before reclassifications, net of tax	(21)	(95)	221
Amortization of net actuarial gain/loss and prior service cost/benefit	21	39	723
Tax expense		(6)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	21	33	723
Total Other comprehensive (loss) income		(62)	944
Balance at end of period	(11)		62
Foreign currency translation
Balance at beginning of period	(2,593)	(2,685)	(2,614)
Other comprehensive (loss) income	(513)	92	(71)
Balance at end of period	(4,194)	(2,593)	(2,685)
Cash flow hedges (P)
Balance at beginning of period	(1,052)	(916)	(1,096)
Net change from periodic revaluations	(93)	(295)	(119)
Tax benefit	7	70	43
Total Other comprehensive (loss) income before reclassifications, net of tax	(86)	(225)	(76)
Net amount reclassified to earnings	288	130	316
Tax expense	(55)	(41)	(60)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	233	89	256
Total Other comprehensive income (loss)	147	(136)	180
Balance at end of period	(905)	(1,052)	(916)
Total Accumulated other comprehensive loss	(5,110)	(3,645)	(3,539)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	290	181	316
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings		(20)
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	(1)	(5)	5
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	(1)	(26)	(5)
Non-controlling Interest [Member]
Pension and other postretirement benefits (O)
Balance at beginning of period	(15)	(5)	(13)
Unrecognized net actuarial gain/loss and prior service cost/benefit	5	(13)	7
Tax (expense) benefit	(2)	2
Total Other comprehensive (loss) income before reclassifications, net of tax	3	(11)	7
Amortization of net actuarial gain/loss and prior service cost/benefit	1	1	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	1	1
Total Other comprehensive (loss) income	4	(10)	8
Acquisition of noncontrolling interest (C)	(1,472)
Balance at end of period		(15)	(5)
Foreign currency translation
Balance at beginning of period	(983)	(1,040)	(937)
Other comprehensive (loss) income	(105)	57	(103)
Balance at end of period		(983)	(1,040)
Cash flow hedges (P)
Balance at beginning of period		1	(1)
Net change from periodic revaluations			2
Total Other comprehensive (loss) income before reclassifications, net of tax			2
Net amount reclassified to earnings		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax		(1)
Total Other comprehensive income (loss)		(1)	2
Balance at end of period			1
Total Accumulated other comprehensive loss		(998)	$ (1,044)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings		$ (1)
Pension and Other Postretirement Benefits attributable to Alcoa Corporation [Member]
Pension and other postretirement benefits (O)
Acquisition of noncontrolling interest (C)	(11)
Pension and Other Postretirement Benefits attributable to Non-controlling interest [Member]
Pension and other postretirement benefits (O)
Acquisition of noncontrolling interest (C)	11
Foreign Currency Translation attributable to Alcoa Corporation [Member]
Pension and other postretirement benefits (O)
Acquisition of noncontrolling interest (C)	(1,088)
Foreign Currency Translation attributable to Non-controlling Interest [Member]
Pension and other postretirement benefits (O)
Acquisition of noncontrolling interest (C)	$ 1,088