Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension and other postretirement benefits
Total Other comprehensive income (loss)	$ 122	$ 124	$ 214	$ 283
Foreign currency translation
Other comprehensive loss	(1,000)	(36)	(464)	(988)
Available-for-sale securities
Other comprehensive (loss) income	(1)	1	0	(1)
Cash flow hedges (P)
Total Other comprehensive (loss) income	(14)	(49)	(11)	135
Alcoa [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,441)	(3,907)	(3,532)	(4,063)
Unrecognized net actuarial loss and prior service cost/benefit	96	46	33	19
Tax (expense) benefit	(33)	(12)	(8)	2
Total Other comprehensive income before reclassifications, net of tax	63	34	25	21
Amortization of net actuarial loss and prior service cost/benefit	97	135	296	395
Tax (expense) benefit	(34)	(47)	(104)	(138)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	63	88	192	257
Total Other comprehensive income (loss)	126	122	217	278
Balance at end of period	(3,315)	(3,785)	(3,315)	(3,785)
Foreign currency translation
Balance at beginning of period	569	428	179	1,147
Other comprehensive loss	(774)	(4)	(384)	(723)
Balance at end of period	(205)	424	(205)	424
Available-for-sale securities
Balance at beginning of period	3	1	2	3
Other comprehensive (loss) income	(1)	1	0	(1)
Balance at end of period	2	2	2	2
Cash flow hedges (P)
Balance at beginning of period	(299)	(305)	(308)	(489)
Net change from periodic revaluations	(35)	(70)	(31)	151
Tax benefit (expense)	11	14	7	(31)
Total Other comprehensive (loss) income before reclassifications, net of tax	(24)	(56)	(24)	120
Net amount reclassified to earnings	6	8	17	16
Tax expense	(1)	(2)	(3)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	5	6	14	14
Total Other comprehensive (loss) income	(19)	(50)	(10)	134
Balance at end of period	(318)	(355)	(318)	(355)
Alcoa [Member] | Aluminum Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	7	5	18	12
Alcoa [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings	(1)	3	(2)	3
Alcoa [Member] | Interest Rate Contracts [Member]
Cash flow hedges (P)
Net amount reclassified to earnings			1	1
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period	(50)	(74)	(51)	(77)
Unrecognized net actuarial loss and prior service cost/benefit	(9)		(9)
Tax (expense) benefit	3		3
Total Other comprehensive income before reclassifications, net of tax	(6)		(6)
Amortization of net actuarial loss and prior service cost/benefit	3	2	5	7
Tax (expense) benefit	(1)		(2)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	2	2	3	5
Total Other comprehensive income (loss)	(4)	2	(3)	5
Balance at end of period	(54)	(72)	(54)	(72)
Foreign currency translation
Balance at beginning of period	36	24	(110)	257
Other comprehensive loss	(226)	(32)	(80)	(265)
Balance at end of period	(190)	(8)	(190)	(8)
Available-for-sale securities
Other comprehensive (loss) income	0	0	0	0
Cash flow hedges (P)
Balance at beginning of period	(8)	(5)	(2)	(5)
Net change from periodic revaluations	7	2	(2)	2
Tax benefit (expense)	(2)	(1)	1	(1)
Total Other comprehensive (loss) income before reclassifications, net of tax	5	1	(1)	1
Total Other comprehensive (loss) income	5	1	(1)	1
Balance at end of period	$ (3)	$ (4)	$ (3)	$ (4)