Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension and other postretirement benefits
Total Other comprehensive (loss) income	$ (2)	$ (82)	$ 557
Foreign currency translation
Other comprehensive loss	(1,995)	(1,266)	(1,335)
Available-for-sale securities
Other comprehensive loss	(5)	(2)	(1)
Cash flow hedges
Total Other comprehensive income (loss)	826	78	184
Energy Contracts [Member]
Cash flow hedges
Total Other comprehensive income before reclassifications, net of tax	(2)	(4)	3
Alcoa [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,601)	(3,532)	(4,063)
Unrecognized net actuarial loss and prior service cost/benefit	(478)	(492)	281
Tax benefit (expense)	170	167	(88)
Total Other comprehensive (loss) income before reclassifications, net of tax	(308)	(325)	193
Amortization of net actuarial loss and prior service cost/benefit	458	394	520
Tax expense	(160)	(138)	(182)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	298	256	338
Total Other comprehensive (loss) income	(10)	(69)	531
Balance at end of period	(3,611)	(3,601)	(3,532)
Foreign currency translation
Balance at beginning of period	(846)	179	1,147
Other comprehensive loss	(1,566)	(1,025)	(968)
Balance at end of period	(2,412)	(846)	179
Available-for-sale securities
Balance at beginning of period		2	3
Other comprehensive loss	(5)	(2)	(1)
Balance at end of period	(5)		2
Cash flow hedges
Balance at beginning of period	(230)	(308)	(489)
Net change from periodic revaluations	1,138	78	205
Tax expense	(340)	(21)	(43)
Total Other comprehensive income before reclassifications, net of tax	798	57	162
Net amount reclassified to earnings	35	25	22
Tax (expense) benefit	(6)	(4)	(3)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	29	21	19
Total Other comprehensive income (loss)	827	78	181
Balance at end of period	597	(230)	(308)
Alcoa [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	21	27	18
Alcoa [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	6
Alcoa [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	5	(3)	2
Alcoa [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1	1	2
Alcoa [Member] | Nickel Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	2
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period	(64)	(51)	(77)
Unrecognized net actuarial loss and prior service cost/benefit	5	(22)	28
Tax benefit (expense)	(1)	7	(9)
Total Other comprehensive (loss) income before reclassifications, net of tax	4	(15)	19
Amortization of net actuarial loss and prior service cost/benefit	6	3	11
Tax expense	(2)	(1)	(4)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	4	2	7
Total Other comprehensive (loss) income	8	(13)	26
Balance at end of period	(56)	(64)	(51)
Foreign currency translation
Balance at beginning of period	(351)	(110)	257
Other comprehensive loss	(429)	(241)	(367)
Balance at end of period	(780)	(351)	(110)
Cash flow hedges
Balance at beginning of period	(2)	(2)	(5)
Net change from periodic revaluations	(1)		4
Tax expense			(1)
Total Other comprehensive income before reclassifications, net of tax	(1)		3
Total Other comprehensive income (loss)	(1)		3
Balance at end of period	$ (3)	$ (2)	$ (2)