Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension and other postretirement benefits
Total Other comprehensive (loss) income	$ (1)	$ 15	$ 106	$ 92
Foreign currency translation
Other comprehensive (loss) income	229	200	(978)	536
Available-for-sale securities
Other comprehensive (loss) income	(2)	1		1
Cash flow hedges
Total Other comprehensive income (loss)	430	(31)	366	3
Energy Contracts [Member]
Cash flow hedges
Total Other comprehensive income (loss) before reclassifications, net of tax	(17)		(11)	5
Alcoa [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,496)	(3,455)	(3,601)	(3,532)
Unrecognized net actuarial loss and prior service cost/benefit	(118)	(80)	(76)	(63)
Tax benefit	39	28	28	25
Total Other comprehensive (loss) income before reclassifications, net of tax	(79)	(52)	(48)	(38)
Amortization of net actuarial loss and prior service cost/benefit	115	101	229	199
Tax expense	(40)	(35)	(80)	(70)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	75	66	149	129
Total Other comprehensive (loss) income	(4)	14	101	91
Balance at end of period	(3,500)	(3,441)	(3,500)	(3,441)
Foreign currency translation
Balance at beginning of period	(1,803)	428	(846)	179
Other comprehensive (loss) income	197	141	(760)	390
Balance at end of period	(1,606)	569	(1,606)	569
Available-for-sale securities
Balance at beginning of period	2	2		2
Other comprehensive (loss) income	(2)	1		1
Balance at end of period		3		3
Cash flow hedges
Balance at beginning of period	(294)	(276)	(230)	(308)
Net change from periodic revaluations	614	(32)	504	4
Tax (expense) benefit	(190)	4	(156)	(4)
Total Other comprehensive income (loss) before reclassifications, net of tax	424	(28)	348
Net amount reclassified to earnings	14	6	29	11
Tax expense	(4)	(1)	(7)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	10	5	22	9
Total Other comprehensive income (loss)	434	(23)	370	9
Balance at end of period	140	(299)	140	(299)
Alcoa [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	10	6	23	11
Alcoa [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	2		4
Alcoa [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1	(1)	1	(1)
Alcoa [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	1	1	1	1
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period	(62)	(51)	(64)	(51)
Unrecognized net actuarial loss and prior service cost/benefit	3		3
Total Other comprehensive (loss) income before reclassifications, net of tax	3		3
Amortization of net actuarial loss and prior service cost/benefit	1	1	4	2
Tax expense	(1)		(2)	(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax		1	2	1
Total Other comprehensive (loss) income	3	1	5	1
Balance at end of period	(59)	(50)	(59)	(50)
Foreign currency translation
Balance at beginning of period	(601)	(23)	(351)	(110)
Other comprehensive (loss) income	32	59	(218)	146
Balance at end of period	(569)	36	(569)	36
Cash flow hedges
Balance at beginning of period	(2)		(2)	(2)
Net change from periodic revaluations	(5)	(12)	(5)	(9)
Tax (expense) benefit	1	4	1	3
Total Other comprehensive income (loss) before reclassifications, net of tax	(4)	(8)	(4)	(6)
Total Other comprehensive income (loss)	(4)	(8)	(4)	(6)
Balance at end of period	$ (6)	$ (8)	$ (6)	$ (8)