Statement of Consolidated Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Sales (C & D)	$ 3,524	$ 3,236	$ 10,542	$ 9,689
Cost of goods sold (exclusive of expenses below)	2,881	2,591	8,552	7,598
Selling, general administrative, and other expenses	134	152	464	569
Research and development expenses	25	24	77	81
Provision for depreciation and amortization	141	140	427	410
Restructuring and other charges (E)	(2)	19	20	118
Operating income	345	310	1,002	913
Interest expense (N)	88	100	291	398
Other expense (income), net (F)	8	38	69	(410)
Income before income taxes	249	172	642	925
Provision for income taxes (H)	88	53	218	272
Net income	161	119	424	653
Amounts Attributable to Arconic Common Shareholders (I):
Net income	$ 160	$ 101	$ 422	$ 600
Earnings per share - basic (in usd per share)	$ 0.33	$ 0.23	$ 0.87	$ 1.36
Earnings per share - diluted (in usd per share)	0.32	0.22	0.86	1.31
Dividends paid per share (in usd per share)	$ 0.06	$ 0.06	$ 0.18	$ 0.18
Average Shares Outstanding (I):
Average shares outstanding - basic (in shares)	483	442	483	441
Average shares outstanding - diluted (in shares)	502	462	503	501