Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension and other postretirement benefits
Total Other comprehensive income	$ 33	$ 107
Foreign currency translation
Other comprehensive income (loss)	410	(1,207)
Available-for-sale securities
Other comprehensive income	1	2
Cash flow hedges
Total Other comprehensive loss	(82)	(64)
Energy Contracts [Member]
Cash flow hedges
Total Other comprehensive loss before reclassifications, net of tax	6	6
Alcoa [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,611)	(3,601)
Unrecognized net actuarial loss and prior service cost/benefit	(59)	42
Tax benefit (expense)	23	(11)
Total Other comprehensive (loss) income before reclassifications, net of tax	(36)	31
Amortization of net actuarial loss and prior service cost/benefit	104	114
Tax expense	(36)	(40)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	68	74
Total Other comprehensive income	32	105
Balance at end of period	(3,579)	(3,496)
Foreign currency translation
Balance at beginning of period	(2,412)	(846)
Other comprehensive income (loss)	303	(957)
Balance at end of period	(2,109)	(1,803)
Available-for-sale securities
Balance at beginning of period	(5)
Other comprehensive income	1	2
Balance at end of period	(4)	2
Cash flow hedges
Balance at beginning of period	597	(230)
Net change from periodic revaluations	(117)	(110)
Tax benefit	37	34
Total Other comprehensive loss before reclassifications, net of tax	(80)	(76)
Net amount reclassified to earnings	(2)	15
Tax benefit (expense)	2	(3)
Total amount reclassified from Accumulated other comprehensive (loss) income, net of tax		12
Total Other comprehensive loss	(80)	(64)
Balance at end of period	517	(294)
Alcoa [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(5)	13
Alcoa [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1	2
Alcoa [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1
Alcoa [Member] | Nickel Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period	(56)	(64)
Amortization of net actuarial loss and prior service cost/benefit	2	3
Tax expense	(1)	(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	2
Total Other comprehensive income	1	2
Balance at end of period	(55)	(62)
Foreign currency translation
Balance at beginning of period	(780)	(351)
Other comprehensive income (loss)	107	(250)
Balance at end of period	(673)	(601)
Cash flow hedges
Balance at beginning of period	(3)	(2)
Net change from periodic revaluations	(3)
Tax benefit	1
Total Other comprehensive loss before reclassifications, net of tax	(2)
Total Other comprehensive loss	(2)
Balance at end of period	$ (5)	$ (2)