Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension and other postretirement benefits
Total Other comprehensive income	$ 31	$ 33
Foreign currency translation
Other comprehensive income	67	410
Available-for-sale securities
Other comprehensive (loss) income	(33)	1
Cash flow hedges
Total Other comprehensive income (loss)	5	(82)
Arconic [Member]
Pension and other postretirement benefits
Balance at beginning of period	(2,010)	(3,611)
Unrecognized net actuarial loss and prior service cost	(6)	(59)
Tax benefit	1	23
Total Other comprehensive loss before reclassifications, net of tax	(5)	(36)
Amortization of net actuarial loss and prior service cost	55	104
Tax expense	(19)	(36)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	36	68
Total Other comprehensive income	31	32
Balance at end of period	(1,979)	(3,579)
Foreign currency translation
Balance at beginning of period	(689)	(2,412)
Other comprehensive income	67	303
Balance at end of period	(622)	(2,109)
Available-for-sale securities
Balance at beginning of period	132	(5)
Other comprehensive (loss) income	(33)	1
Balance at end of period	99	(4)
Cash flow hedges
Balance at beginning of period	(1)	597
Net change from periodic revaluations	8	(117)
Tax (expense) benefit	(3)	37
Total Other comprehensive income (loss) before reclassifications, net of tax	5	(80)
Net amount reclassified to earnings		(2)
Tax benefit		2
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	0
Total Other comprehensive income (loss)	5	(80)
Balance at end of period	4	517
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period		(56)
Amortization of net actuarial loss and prior service cost		2
Tax expense		(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax		1
Total Other comprehensive income		1
Balance at end of period		(55)
Foreign currency translation
Balance at beginning of period	(2)	(780)
Other comprehensive income		107
Balance at end of period	(2)	(673)
Cash flow hedges
Balance at beginning of period		(3)
Net change from periodic revaluations		(3)
Tax (expense) benefit		1
Total Other comprehensive income (loss) before reclassifications, net of tax		(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	$ 0	0
Total Other comprehensive income (loss)		(2)
Balance at end of period		$ (5)