Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Pension and other postretirement benefits (L)
Total Other comprehensive income (loss)	$ 1	$ (4)	$ (27)	$ (16)
Acquisition of noncontrolling interest (C)	(288)
Foreign currency translation
Other comprehensive income (loss)	109	(114)	(143)	(61)
Cash flow hedges (M)
Net change from periodic revaluations	(143)	(120)	(179)	(66)
Net amount reclassified to earnings	74	29	201	93
Total Accumulated other comprehensive loss	(4,742)		(4,742)		$ (3,645)
Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	22	76		62
Unrecognized net actuarial gain/loss and prior service cost/benefit	(5)		9	(18)
Tax (expense) benefit	1		(2)	8
Total Other comprehensive income (loss) before reclassifications, net of tax	(4)		7	(10)
Amortization of net actuarial gain/loss and prior service cost/benefit	5	5	16	35
Tax benefit (expense)				(6)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	5	5	16	29
Total Other comprehensive income (loss)	1	5	23	19
Balance at end of period	12	81	12	81
Foreign currency translation
Balance at beginning of period	(2,775)	(2,658)	(2,593)	(2,685)
Other comprehensive income (loss)	144	(67)	(38)	(40)
Balance at end of period	(3,719)	(2,725)	(3,719)	(2,725)
Cash flow hedges (M)
Balance at beginning of period	(984)	(812)	(1,052)	(916)
Net change from periodic revaluations	(143)	(120)	(179)	(66)
Tax benefit	33	16	33	16
Total Other comprehensive loss before reclassifications, net of tax	(110)	(104)	(146)	(50)
Net amount reclassified to earnings	74	29	201	93
Tax expense	(15)	(16)	(38)	(30)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	59	13	163	63
Total Other comprehensive (loss) income	(51)	(91)	17	13
Balance at end of period	(1,035)	(903)	(1,035)	(903)
Total Accumulated other comprehensive loss	(4,742)	(3,547)	(4,742)	(3,547)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	73	42	205	136
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		(3)	(1)	(5)
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	1	(10)	(3)	(18)
Pension and Other Postretirement Benefits attributable to Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Acquisition of noncontrolling interest (C)	(11)		(11)
Foreign Currency Translation attributable to Alcoa Corporation [Member]
Pension and other postretirement benefits (L)
Acquisition of noncontrolling interest (C)	(1,088)		(1,088)
Non-controlling Interest [Member]
Pension and other postretirement benefits (L)
Balance at beginning of period	(9)	(7)	(15)	(5)
Unrecognized net actuarial gain/loss and prior service cost/benefit	(2)	(1)	5	(3)
Tax (expense) benefit			(2)
Total Other comprehensive income (loss) before reclassifications, net of tax	(2)	(1)	3	(3)
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)	(2)	(1)	4	(3)
Acquisition of noncontrolling interest (C)	(1,472)
Balance at end of period		(8)		(8)
Foreign currency translation
Balance at beginning of period	(1,053)	(1,014)	(983)	(1,040)
Other comprehensive income (loss)	(35)	(47)	(105)	(21)
Balance at end of period		(1,061)		(1,061)
Cash flow hedges (M)
Balance at beginning of period	(1)	1		1
Net amount reclassified to earnings	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1
Total Other comprehensive (loss) income	1
Balance at end of period		1		1
Total Accumulated other comprehensive loss		$ (1,068)		$ (1,068)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges (M)
Net amount reclassified to earnings	1
Pension and Other Postretirement Benefits attributable to Non-controlling interest [Member]
Pension and other postretirement benefits (L)
Acquisition of noncontrolling interest (C)	11		11
Foreign Currency Translation attributable to Non-controlling Interest [Member]
Pension and other postretirement benefits (L)
Acquisition of noncontrolling interest (C)	$ 1,088		$ 1,088