Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Apr. 01, 2019	Jan. 01, 2019	Apr. 01, 2018	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,178	$ 5,282	$ 5,585	$ 4,924
Other comprehensive income:
Total Other comprehensive (loss) income, net of tax	(17)	(170)	59	88
Adoption of accounting standards (B)						$ 73
Balance at end of period	4,866	5,218	4,866	5,218
Arconic
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,852)	(2,386)	(2,926)	(2,644)
Other comprehensive income:
Total Other comprehensive (loss) income, net of tax	(17)	(170)	59	88
Adoption of accounting standards (B)						(2)
Balance at end of period	(2,869)	(2,556)	(2,869)	(2,556)
Pension and other postretirement benefits (F)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,304)	(2,087)	(2,344)	(2,230)
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	(6)	(15)	66	122
Tax benefit (expense)	1	3	(15)	(28)
Total Other comprehensive loss before reclassifications, net of tax	(5)	(12)	51	94
Amortization of net actuarial loss and prior service cost	36	52	15	100
Tax benefit (expense)	(8)	(11)	(3)	(22)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	28	41	12	78
Total Other comprehensive (loss) income, net of tax	23	29	63	172
Balance at end of period	(2,281)	(2,058)	(2,281)	(2,058)
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(557)	(315)	(583)	(437)
Other comprehensive income:
Total Other comprehensive (loss) income, net of tax	(30)	(201)	(4)	(79)
Balance at end of period	(587)	(516)	(587)	(516)
Available-for-sale securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	(2)	(3)	(2)
Other comprehensive income:
Total Other comprehensive (loss) income, net of tax	0	(2)	3	(2)
Balance at end of period	0	(4)	0	(4)
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	9	18	4	25
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	(13)	9	(5)	3
Tax benefit (expense)	3	(1)	2	0
Total Other comprehensive loss before reclassifications, net of tax	(10)	8	(3)	3
Amortization of net actuarial loss and prior service cost	(1)	(4)	(1)	(7)
Tax benefit (expense)	1	0	1	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	(4)	0	(6)
Total Other comprehensive (loss) income, net of tax	(10)	4	(3)	(3)
Balance at end of period	$ (1)	$ 22	$ (1)	$ 22
Accounting Standards Update 2017-12
Other comprehensive income:
Adoption of accounting standards (B)						2
Accounting Standards Update 2017-12 | Cash flow hedges
Other comprehensive income:
Adoption of accounting standards (B)					$ 0	$ (2)	$ 0	$ 0