Statement of Consolidated Comprehensive (Loss) Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net (loss) income	$ (74)	$ (878)	$ (197)
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(220)	(482)	(2)
Foreign currency translation adjustments	254	450	(1,995)
Net change in unrealized gains on available-for-sale securities	(134)	137	(5)
Net change in unrecognized gains (losses) on cash flow hedges	26	(612)	826
Total Other comprehensive (loss) income, net of tax	(74)	(507)	(1,176)
Comprehensive (loss) income	(148)	(1,385)	(1,373)
Arconic
Net (loss) income	(74)	(941)	(322)
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(220)	(479)	(10)
Foreign currency translation adjustments	252	268	(1,566)
Net change in unrealized gains on available-for-sale securities	(134)	137	(5)
Net change in unrecognized gains (losses) on cash flow hedges	26	(617)	827
Total Other comprehensive (loss) income, net of tax	(76)	(691)	(754)
Comprehensive (loss) income	(150)	(1,632)	(1,076)
Noncontrolling Interests
Net (loss) income	0	63	125
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	0	(3)	8
Foreign currency translation adjustments	2	182	(429)
Net change in unrealized gains on available-for-sale securities	0	0	0
Net change in unrecognized gains (losses) on cash flow hedges	0	5	(1)
Total Other comprehensive (loss) income, net of tax	2	184	(422)
Comprehensive (loss) income	$ 2	$ 247	$ (297)