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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension and other postretirement benefits
Total Other comprehensive income	$ 48	$ 67	$ 79	$ 100
Foreign currency translation
Other comprehensive income	99	77	166	487
Available-for-sale securities
Other comprehensive (loss) income	(101)	3	(134)	4
Cash flow hedges
Total Other comprehensive income (loss)	(2)	(137)	3	(219)
Arconic [Member]
Pension and other postretirement benefits
Balance at beginning of period	(1,979)	(3,579)	(2,010)	(3,611)
Unrecognized net actuarial loss and prior service cost	17	(5)	11	(64)
Tax (expense) benefit	(5)	3	(4)	26
Total Other comprehensive loss before reclassifications, net of tax	12	(2)	7	(38)
Amortization of net actuarial loss and prior service cost	56	104	111	208
Tax (expense) benefit	(20)	(37)	(39)	(73)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	36	67	72	135
Total Other comprehensive income	48	65	79	97
Balance at end of period	(1,931)	(3,514)	(1,931)	(3,514)
Foreign currency translation
Balance at beginning of period	(622)	(2,109)	(689)	(2,412)
Other comprehensive income	99	45	166	348
Balance at end of period	(523)	(2,064)	(523)	(2,064)
Available-for-sale securities
Balance at beginning of period	99	(4)	132	(5)
Other comprehensive (loss) income	(101)	3	(134)	4
Balance at end of period	(2)	(1)	(2)	(1)
Cash flow hedges
Balance at beginning of period	4	517	(1)	597
Net change from periodic revaluations	(4)	(225)	4	(342)
Tax (expense) benefit	1	66	(2)	103
Total Other comprehensive income (loss) before reclassifications, net of tax	(3)	(159)	2	(239)
Net amount reclassified to earnings	1	7	1	5
Tax benefit (expense)		(1)		1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1	6	1	6
Total Other comprehensive income (loss)	(2)	(153)	3	(233)
Balance at end of period	2	364	2	364
Noncontrolling Interests [Member]
Pension and other postretirement benefits
Balance at beginning of period		(55)		(56)
Unrecognized net actuarial loss and prior service cost		1		1
Total Other comprehensive loss before reclassifications, net of tax		1		1
Amortization of net actuarial loss and prior service cost				2
Tax (expense) benefit		1
Total amount reclassified from Accumulated other comprehensive loss, net of tax		1		2
Total Other comprehensive income		2		3
Balance at end of period		(53)		(53)
Foreign currency translation
Balance at beginning of period	(2)	(673)	(2)	(780)
Other comprehensive income		32		139
Balance at end of period	$ (2)	(641)	$ (2)	(641)
Cash flow hedges
Balance at beginning of period		(5)		(3)
Net change from periodic revaluations		18		15
Tax (expense) benefit		(5)		(4)
Total Other comprehensive income (loss) before reclassifications, net of tax		13		11
Net amount reclassified to earnings		5		5
Tax benefit (expense)		(2)		(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax		3		3
Total Other comprehensive income (loss)		16		14
Balance at end of period		$ 11		$ 11