Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Pension and other postretirement benefits (L)
Total Other comprehensive income	$ (5)	$ (10)
Foreign currency translation
Other comprehensive income (loss)	185	(176)
Joint venture formation (C)	(76)
Cash flow hedges (M)
Net change from periodic revaluations	(85)	117
Net amount reclassified to earnings	95	53
Total Accumulated other comprehensive loss	(4,935)		$ (5,110)
Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	(11)	0
Unrecognized net actuarial gain/loss and prior service cost/benefit	(1)	4
Tax expense	(1)	(1)
Total Other comprehensive (loss) income before reclassifications, net of tax	(2)	3
Amortization of net actuarial gain/loss and prior service cost/benefit	7	6
Total amount reclassified from Accumulated other comprehensive loss, net of tax	7	6
Total Other comprehensive income	5	9
Balance at end of period	(6)	9
Foreign currency translation
Balance at beginning of period	(4,194)	(2,593)
Other comprehensive income (loss)	185	(122)
Joint venture formation (C)	(31)
Balance at end of period	(4,040)	(2,715)
Cash flow hedges (M)
Balance at beginning of period	(905)	(1,052)
Net change from periodic revaluations	(85)	117
Tax benefit (expense)	23	(31)
Total Other comprehensive (loss) income before reclassifications, net of tax	(62)	86
Net amount reclassified to earnings	95	53
Tax expense	(17)	(9)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	78	44
Total Other comprehensive income	16	130
Balance at end of period	(889)	(922)
Total Accumulated other comprehensive loss	(4,935)	(3,628)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	93	57
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	$ 2	(4)
Non-controlling Interest [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period		(15)
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		1
Balance at end of period		(14)
Foreign currency translation
Balance at beginning of period		(983)
Other comprehensive income (loss)		(54)
Balance at end of period		(1,037)
Cash flow hedges (M)
Total Accumulated other comprehensive loss		$ (1,051)