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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension and other postretirement benefits
Total Other comprehensive income (loss)	$ 49	$ 19	$ 214	$ 21
Foreign currency translation
Other comprehensive income	185	77	402	630
Cash flow hedges
Total Other comprehensive (loss) income before reclassifications, net of tax	12		12
Total Other comprehensive (loss) income	(420)	(380)	(672)	(635)
Alcoa Corporation [Member]
Pension and other postretirement benefits
Balance at beginning of period	(2,184)	(353)	(2,330)	(352)
Establishment of defined benefit plans		(2,704)		(2,704)
Unrecognized net actuarial loss and prior service cost/benefit	(6)	(22)	42	(44)
Tax benefit (expense)	2	17	5	25
Total Other comprehensive (loss) income before reclassifications, net of tax	(4)	(5)	47	(19)
Amortization of net actuarial loss and prior service cost/benefit	50	38	149	58
Tax expense	(2)	(13)	(6)	(20)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	48	25	143	38
Total Other comprehensive income (loss)	44	20	190	19
Balance at end of period	(2,140)	(3,037)	(2,140)	(3,037)
Foreign currency translation
Balance at beginning of period	(1,515)	(1,437)	(1,655)	(1,851)
Other comprehensive income	141	32	281	446
Balance at end of period	(1,374)	(1,405)	(1,374)	(1,405)
Cash flow hedges
Balance at beginning of period	(104)	334	210	603
Net change from periodic revaluations	(545)	(434)	(975)	(779)
Tax benefit (expense)	109	95	186	170
Total Other comprehensive (loss) income before reclassifications, net of tax	(436)	(339)	(789)	(609)
Net amount reclassified to earnings	25	(46)	71	(44)
Tax (expense) benefit	(4)	15	(11)	14
Total amount reclassified from Accumulated other comprehensive (loss) income, net of tax	21	(31)	60	(30)
Total Other comprehensive (loss) income	(415)	(370)	(729)	(639)
Balance at end of period	(519)	(36)	(519)	(36)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	33	4	82	(1)
Alcoa Corporation [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(8)	(50)	(11)	(50)
Alcoa Corporation [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings				7
Non-controlling Interest [Member]
Pension and other postretirement benefits
Balance at beginning of period	(37)	(53)	(56)	(56)
Unrecognized net actuarial loss and prior service cost/benefit	6	(1)	24
Tax benefit (expense)	(2)		(2)
Total Other comprehensive (loss) income before reclassifications, net of tax	4	(1)	22
Amortization of net actuarial loss and prior service cost/benefit	1	1	2	3
Tax expense		(1)		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1		2	2
Total Other comprehensive income (loss)	5	(1)	24	2
Balance at end of period	(32)	(54)	(32)	(54)
Foreign currency translation
Balance at beginning of period	(600)	(640)	(677)	(779)
Other comprehensive income	44	45	121	184
Balance at end of period	(556)	(595)	(556)	(595)
Cash flow hedges
Balance at beginning of period	63	11	1	(3)
Net change from periodic revaluations	(2)	20	88	35
Tax benefit (expense)	1	(6)	(26)	(10)
Total Other comprehensive (loss) income before reclassifications, net of tax	(1)	14	62	25
Net amount reclassified to earnings	(5)	(34)	(7)	(29)
Tax (expense) benefit	1	10	2	8
Total amount reclassified from Accumulated other comprehensive (loss) income, net of tax	(4)	(24)	(5)	(21)
Total Other comprehensive (loss) income	(5)	(10)	57	4
Balance at end of period	58	1	58	1
Non-controlling Interest [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	$ (5)	$ (34)	$ (7)	(34)
Non-controlling Interest [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings				$ 5