Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension and other postretirement benefits
Total Other comprehensive income	$ 67	$ (1)	$ 100	$ 106
Foreign currency translation
Other comprehensive income	77	229	487	(978)
Available-for-sale securities
Other comprehensive income	3	(2)	4
Cash flow hedges
Total Other comprehensive (loss) income	(137)	430	(219)	366
Energy Contracts [Member]
Cash flow hedges
Total Other comprehensive (loss) income before reclassifications, net of tax	45	(17)	39	(11)
Alcoa [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,579)	(3,496)	(3,611)	(3,601)
Unrecognized net actuarial loss and prior service cost/benefit	(5)	(118)	(64)	(76)
Tax benefit	3	39	26	28
Total Other comprehensive (loss) income before reclassifications, net of tax	(2)	(79)	(38)	(48)
Amortization of net actuarial loss and prior service cost/benefit	104	115	208	229
Tax (expense) benefit	(37)	(40)	(73)	(80)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	67	75	135	149
Total Other comprehensive income	65	(4)	97	101
Balance at end of period	(3,514)	(3,500)	(3,514)	(3,500)
Foreign currency translation
Balance at beginning of period	(2,109)	(1,803)	(2,412)	(846)
Other comprehensive income	45	197	348	(760)
Balance at end of period	(2,064)	(1,606)	(2,064)	(1,606)
Available-for-sale securities
Balance at beginning of period	(4)	2	(5)
Other comprehensive income	3	(2)	4
Balance at end of period	(1)		(1)
Cash flow hedges
Balance at beginning of period	517	(294)	597	(230)
Net change from periodic revaluations	(225)	614	(342)	504
Tax benefit (expense)	66	(190)	103	(156)
Total Other comprehensive (loss) income before reclassifications, net of tax	(159)	424	(239)	348
Net amount reclassified to earnings	7	14	(5)	29
Tax benefit (expense)	(1)	(4)	1	(7)
Total amount reclassified from Accumulated other comprehensive income (loss), net of tax	6	10	6	22
Total Other comprehensive (loss) income	(153)	434	(233)	370
Balance at end of period	364	140	364	140
Alcoa [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(1)	10	(6)	23
Alcoa [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings		2	1	4
Alcoa [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings		1	1	1
Alcoa [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	8	1	8	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	(55)	(62)	(56)	(64)
Unrecognized net actuarial loss and prior service cost/benefit	1	3	1	3
Total Other comprehensive (loss) income before reclassifications, net of tax	1	3	1	3
Amortization of net actuarial loss and prior service cost/benefit		1	2	4
Tax (expense) benefit	1	(1)		(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1		2	2
Total Other comprehensive income	2	3	3	5
Balance at end of period	(53)	(59)	(53)	(59)
Foreign currency translation
Balance at beginning of period	(673)	(601)	(780)	(351)
Other comprehensive income	32	32	139	(218)
Balance at end of period	(641)	(569)	(641)	(569)
Cash flow hedges
Balance at beginning of period	(5)	(2)	(3)	(2)
Net change from periodic revaluations	18	(5)	15	(5)
Tax benefit (expense)	(5)	1	(4)	1
Total Other comprehensive (loss) income before reclassifications, net of tax	13	(4)	11	(4)
Net amount reclassified to earnings	5		5
Tax benefit (expense)	(2)		(2)
Total amount reclassified from Accumulated other comprehensive income (loss), net of tax	3		3
Total Other comprehensive (loss) income	16	(4)	14	(4)
Balance at end of period	11	$ (6)	11	$ (6)
Noncontrolling Interests [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	$ 5		$ 5