Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Pension and other postretirement benefits (K)
Total Other comprehensive income	$ (23)	$ (132)
Foreign currency translation
Other comprehensive income (loss)	424	(236)
Cash flow hedges (L)
Net change from periodic revaluations	(1,063)	(303)
Net amount reclassified to earnings	114	52
Total Accumulated other comprehensive loss	(5,074)		$ (4,592)
Alcoa Corporation [Member]
Pension and other postretirement benefits (K)
Balance at beginning of period	(882)	(2,536)
Unrecognized net actuarial loss and prior service cost/benefit	(7)	69
Tax benefit	1	2
Total Other comprehensive (loss) income before reclassifications, net of tax	(6)	71
Amortization of net actuarial loss and prior service cost/benefit	28	61
Tax expense		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	28	60
Total Other comprehensive income	22	131
Balance at end of period	(860)	(2,405)
Foreign currency translation
Balance at beginning of period	(2,614)	(2,385)
Other comprehensive income (loss)	326	(176)
Balance at end of period	(2,288)	(2,561)
Cash flow hedges (L)
Balance at beginning of period	(1,096)	(708)
Net change from periodic revaluations	(1,063)	(303)
Tax benefit	153	56
Total Other comprehensive (loss) income before reclassifications, net of tax	(910)	(247)
Net amount reclassified to earnings	114	52
Tax expense	(34)	(9)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	80	43
Total Other comprehensive (loss) income	(830)	(204)
Balance at end of period	(1,926)	(912)
Total Accumulated other comprehensive loss	(5,074)	(5,878)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings	110	41
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings		9
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings	4	3
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (L)
Net amount reclassified to earnings		(1)
Non-controlling Interest [Member]
Pension and other postretirement benefits (K)
Balance at beginning of period	(13)	(67)
Amortization of net actuarial loss and prior service cost/benefit	1	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	1
Total Other comprehensive income	1	1
Balance at end of period	(12)	(66)
Foreign currency translation
Balance at beginning of period	(937)	(844)
Other comprehensive income (loss)	98	(60)
Balance at end of period	(839)	(904)
Cash flow hedges (L)
Balance at beginning of period	(1)	(1)
Net change from periodic revaluations	1	(10)
Tax benefit		3
Total Other comprehensive (loss) income before reclassifications, net of tax	1	(7)
Net amount reclassified to earnings		6
Tax expense		(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax		4
Total Other comprehensive (loss) income	1	(3)
Balance at end of period		(4)
Total Accumulated other comprehensive loss	$ (851)	(974)
Non-controlling Interest [Member] | Financial Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings		$ 6