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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Pension and other postretirement benefits (K)
Total Other comprehensive income	$ (662)	$ (84)	$ (737)	$ (472)
Foreign currency translation
Other comprehensive loss	(254)	(280)	(332)	(261)
Cash flow hedges (L)
Net change from periodic revaluations	110	(222)	231	(922)
Net amount reclassified to earnings	37	82	280	201
Total Accumulated other comprehensive loss	(3,644)		(3,644)		$ (4,592)
Alcoa Corporation [Member]
Pension and other postretirement benefits (K)
Balance at beginning of period	(808)	(2,152)	(882)	(2,536)
Unrecognized net actuarial loss and prior service cost/benefit	17	26	40	259
Tax expense	(7)	(9)	(12)	(7)
Total Other comprehensive income before reclassifications, net of tax	10	17	28	252
Amortization of net actuarial loss and prior service cost/benefit	645	56	702	206
Tax benefit (expense)	1	(1)		(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	646	55	702	204
Total Other comprehensive income	656	72	730	456
Balance at end of period	(152)	(2,080)	(152)	(2,080)
Foreign currency translation
Balance at beginning of period	(2,658)	(2,357)	(2,614)	(2,385)
Other comprehensive loss	(173)	(202)	(217)	(174)
Balance at end of period	(2,831)	(2,559)	(2,831)	(2,559)
Cash flow hedges (L)
Balance at beginning of period	(789)	(1,178)	(1,096)	(708)
Net change from periodic revaluations	110	(222)	231	(922)
Tax (expense) benefit	(6)	38	(17)	169
Total Other comprehensive income (loss) before reclassifications, net of tax	104	(184)	214	(753)
Net amount reclassified to earnings	37	82	280	201
Tax (expense) benefit	(13)	(9)	(59)	(29)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	24	73	221	172
Total Other comprehensive income (loss)	128	(111)	435	(581)
Balance at end of period	(661)	(1,289)	(661)	(1,289)
Total Accumulated other comprehensive loss	(3,644)	(5,928)	(3,644)	(5,928)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings	35	82	277	195
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings		(3)		2
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings	2	3	6	7
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges (L)
Net amount reclassified to earnings			(3)	(3)
Non-controlling Interest [Member]
Pension and other postretirement benefits (K)
Balance at beginning of period	(12)	(63)	(13)	(67)
Unrecognized net actuarial loss and prior service cost/benefit	8	14	9	16
Tax expense	(3)	(4)	(3)	(4)
Total Other comprehensive income before reclassifications, net of tax	5	10	6	12
Amortization of net actuarial loss and prior service cost/benefit	1	2	1	4
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	2	1	4
Total Other comprehensive income	6	12	7	16
Balance at end of period	(6)	(51)	(6)	(51)
Foreign currency translation
Balance at beginning of period	(971)	(853)	(937)	(844)
Other comprehensive loss	(81)	(78)	(115)	(87)
Balance at end of period	(1,052)	(931)	(1,052)	(931)
Cash flow hedges (L)
Balance at beginning of period	1	1	(1)	(1)
Net change from periodic revaluations		(1)	2	(2)
Tax (expense) benefit		1		1
Total Other comprehensive income (loss) before reclassifications, net of tax			2	(1)
Net amount reclassified to earnings		(3)		1
Tax (expense) benefit		1
Total amount reclassified from Accumulated other comprehensive loss, net of tax		(2)		1
Total Other comprehensive income (loss)		(2)	2
Balance at end of period	1	(1)	1	(1)
Total Accumulated other comprehensive loss	$ (1,057)	(983)	$ (1,057)	(983)
Non-controlling Interest [Member] | Financial Contracts [Member]
Cash flow hedges (L)
Net amount reclassified to earnings		$ (3)		$ 1