Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension and other postretirement benefits (O)
Total Other comprehensive income (loss)	$ (1,708)	$ 265	$ 9
Foreign currency translation
Other comprehensive loss	(322)	(235)	(113)
Cash flow hedges (P)
Net change from periodic revaluations	(782)	(345)
Net amount reclassified to earnings	295	106
Total Accumulated other comprehensive loss	(4,592)	(5,629)
Alcoa Corporation [Member]
Pension and other postretirement benefits (O)
Balance at beginning of period	(2,536)	(2,282)	(2,283)
Unrecognized net actuarial gain (loss) and prior service cost/benefit	550	(545)	(309)
Tax (expense) benefit	(37)	31	28
Total Other comprehensive income (loss) before reclassifications, net of tax	513	(514)	(281)
Amortization of net actuarial loss and prior service cost/benefit	1,144	269	299
Tax expense	(3)	(9)	(17)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1,141	260	282
Total Other comprehensive income (loss)	1,654	(254)	1
Balance at end of period	(882)	(2,536)	(2,282)
Foreign currency translation
Balance at beginning of period	(2,385)	(2,160)	(2,071)
Other comprehensive loss	(229)	(225)	(89)
Balance at end of period	(2,614)	(2,385)	(2,160)
Cash flow hedges (P)
Balance at beginning of period	(708)	(532)	(211)
Net change from periodic revaluations	(782)	(345)	(437)
Tax benefit (expense)	140	74	83
Total Other comprehensive (loss) income before reclassifications, net of tax	(642)	(271)	(354)
Net amount reclassified to earnings	295	106	23
Tax (expense) benefit	(41)	(11)	10
Total amount reclassified from Accumulated other comprehensive loss, net of tax	254	95	33
Total Other comprehensive loss	(388)	(176)	(321)
Balance at end of period	(1,096)	(708)	(532)
Total Accumulated other comprehensive loss	(4,592)	(5,629)	(4,974)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	288	66	44
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	2	15	(43)
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	(3)	20	18
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	8	5	4
Non-controlling Interest [Member]
Pension and other postretirement benefits (O)
Balance at beginning of period	(67)	(56)	(46)
Unrecognized net actuarial gain (loss) and prior service cost/benefit	30	(19)	(14)
Tax (expense) benefit	(6)	3
Total Other comprehensive income (loss) before reclassifications, net of tax	24	(16)	(14)
Amortization of net actuarial loss and prior service cost/benefit	30	6	5
Tax expense		(1)	(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	30	5	4
Total Other comprehensive income (loss)	54	(11)	(10)
Balance at end of period	(13)	(67)	(56)
Foreign currency translation
Balance at beginning of period	(844)	(834)	(810)
Other comprehensive loss	(93)	(10)	(24)
Balance at end of period	(937)	(844)	(834)
Cash flow hedges (P)
Balance at beginning of period	(1)	20	31
Net change from periodic revaluations	(2)	(36)	20
Tax benefit (expense)	1	10	(6)
Total Other comprehensive (loss) income before reclassifications, net of tax	(1)	(26)	14
Net amount reclassified to earnings	2	6	(35)
Tax (expense) benefit	(1)	(1)	10
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	5	(25)
Total Other comprehensive loss		(21)	(11)
Balance at end of period	(1)	(1)	20
Total Accumulated other comprehensive loss	(951)	(912)	(870)
Non-controlling Interest [Member] | Financial Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	1	$ 6	$ (35)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	$ 1