Accumulated Other Comprehensive (Loss) Income - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Pension and other postretirement benefits (L)
Total Other comprehensive income	$ (11)		$ (18)	$ (16)	$ (28)
Foreign currency translation
Other comprehensive income (loss)	217		(76)	402	(252)
Joint venture formation (C)		$ (76)
Cash flow hedges (M)
Net change from periodic revaluations	(128)		(153)	(213)	(36)
Net amount reclassified to earnings	80		74	175	127
Total Accumulated other comprehensive (loss) income	(4,764)			(4,764)		$ (5,110)
Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	(6)	(11)	9	(11)
Unrecognized net actuarial gain/loss and prior service cost/benefit	1		10		14
Tax benefit (expense)	3		(2)	2	(3)
Total Other comprehensive income before reclassifications, net of tax	4		8	2	11
Amortization of net actuarial gain/loss and prior service cost/benefit	7		5	14	11
Total amount reclassified from Accumulated other comprehensive loss, net of tax	7		5	14	11
Total Other comprehensive income	11		13	16	22
Balance at end of period	5	(6)	22	5	22
Foreign currency translation
Balance at beginning of period	(4,040)	(4,194)	(2,715)	(4,194)	(2,593)
Other comprehensive income (loss)	207		(60)	392	(182)
Joint venture formation (C)				(31)
Balance at end of period	(3,833)	(4,040)	(2,775)	(3,833)	(2,775)
Cash flow hedges (M)
Balance at beginning of period	(889)	(905)	(922)	(905)	(1,052)
Net change from periodic revaluations	(128)		(153)	(213)	(36)
Tax benefit	18		31	41
Total Other comprehensive loss before reclassifications, net of tax	(110)		(122)	(172)	(36)
Net amount reclassified to earnings	80		74	175	127
Tax expense	(17)		(14)	(34)	(23)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	63		60	141	104
Total Other comprehensive (loss) income	(47)		(62)	(31)	68
Balance at end of period	(936)	$ (889)	(984)	(936)	(984)
Total Accumulated other comprehensive (loss) income	(4,764)		(3,737)	(4,764)	(3,737)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	78		75	171	132
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	2			2
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings			(1)		(1)
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			(14)		(15)
Unrecognized net actuarial gain/loss and prior service cost/benefit			7		7
Tax benefit (expense)			(2)		(2)
Total Other comprehensive income before reclassifications, net of tax			5		5
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			5		6
Balance at end of period			(9)		(9)
Foreign currency translation
Balance at beginning of period			(1,037)		(983)
Other comprehensive income (loss)	10		(16)	10	(70)
Balance at end of period	10		(1,053)	10	(1,053)
Cash flow hedges (M)
Net amount reclassified to earnings			(1)		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax			(1)		(1)
Total Other comprehensive (loss) income			(1)		(1)
Balance at end of period			(1)		(1)
Total Accumulated other comprehensive (loss) income	$ 10		(1,063)	$ 10	(1,063)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings			$ (1)		$ (1)