Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension and other postretirement benefits
Total Other comprehensive (loss) income	$ (463)	$ 120	$ (363)	$ 226
Foreign currency translation
Other comprehensive income (loss)	202	(1,188)	689	(2,166)
Available-for-sale securities
Other comprehensive income (loss)		(2)	4	(2)
Cash flow hedges
Total Other comprehensive (loss) income	(348)	215	(567)	581
Energy Contracts [Member]
Cash flow hedges
Total Other comprehensive (loss) income before reclassifications, net of tax	49	3	88	(8)
Arconic [Member]
Pension and other postretirement benefits
Balance at beginning of period	(3,514)	(3,500)	(3,611)	(3,601)
Unrecognized net actuarial loss and prior service cost/benefit	(819)	46	(883)	(30)
Tax benefit (expense)	(286)	10	312	18
Total Other comprehensive (loss) income before reclassifications, net of tax	(533)	36	(571)	(12)
Amortization of net actuarial loss and prior service cost/benefit	109	116	317	345
Tax expense	(38)	(41)	(111)	(121)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	71	75	206	224
Total Other comprehensive (loss) income	(462)	111	(365)	212
Balance at end of period	(3,976)	(3,389)	(3,976)	(3,389)
Foreign currency translation
Balance at beginning of period	(2,064)	(1,606)	(2,412)	(846)
Other comprehensive income (loss)	157	(889)	505	(1,649)
Balance at end of period	(1,907)	(2,495)	(1,907)	(2,495)
Available-for-sale securities
Balance at beginning of period	(1)		(5)
Other comprehensive income (loss)		(2)	4	(2)
Balance at end of period	(1)	(2)	(1)	(2)
Cash flow hedges
Balance at beginning of period	364	140	597	(230)
Net change from periodic revaluations	(430)	288	(772)	792
Tax benefit (expense)	126	(79)	229	(235)
Total Other comprehensive (loss) income before reclassifications, net of tax	(304)	209	(543)	557
Net amount reclassified to earnings	(46)	6	(41)	35
Tax benefit (expense)	12	(1)	13	(8)
Total amount reclassified from Accumulated other comprehensive (loss) income, net of tax	(34)	5	(28)	27
Total Other comprehensive (loss) income	(338)	214	(571)	584
Balance at end of period	26	354	26	354
Arconic [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	5	3	(1)	26
Arconic [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(50)		(49)	4
Arconic [Member] | Foreign Exchange Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(1)	2		3
Arconic [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings			8	1
Arconic [Member] | Nickel Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings		1	1	1
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period	(53)	(59)	(56)	(64)
Unrecognized net actuarial loss and prior service cost/benefit	(1)	10		13
Tax benefit (expense)		1		(1)
Total Other comprehensive (loss) income before reclassifications, net of tax	(1)	9		12
Amortization of net actuarial loss and prior service cost/benefit	1		3	4
Tax expense	(1)		(1)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax			2	2
Total Other comprehensive (loss) income	(1)	9	2	14
Balance at end of period	(54)	(50)	(54)	(50)
Foreign currency translation
Balance at beginning of period	(641)	(569)	(780)	(351)
Other comprehensive income (loss)	45	(299)	184	(517)
Balance at end of period	(596)	(868)	(596)	(868)
Cash flow hedges
Balance at beginning of period	11	(6)	(3)	(2)
Net change from periodic revaluations	20	1	35	(4)
Tax benefit (expense)	(6)		(10)	1
Total Other comprehensive (loss) income before reclassifications, net of tax	14	1	25	(3)
Net amount reclassified to earnings	(34)		(29)
Tax benefit (expense)	10		8
Total amount reclassified from Accumulated other comprehensive (loss) income, net of tax	(24)		(21)
Total Other comprehensive (loss) income	(10)	1	4	(3)
Balance at end of period	1	$ (5)	1	$ (5)
Noncontrolling Interests [Member] | Energy Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	$ (34)		(34)
Noncontrolling Interests [Member] | Interest Rate Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings			$ 5