Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income from continuing operations attributable to common shareholders	$ 27	$ 36	$ 181	$ 105
Income from discontinued operations	0	0	0	50
Net income	27	36	181	155
Less: preferred stock dividends declared	1	1	2	2
Net income available to Howmet Aerospace common shareholders - basic	26	35	179	153
Net income available to Howmet Aerospace common shareholders - diluted	$ 26	$ 35	$ 179	$ 153
Average shares outstanding - basic (in shares)	429	436	431	436
Effect of dilutive securities:
Stock options (in shares)	1	0	1	0
Stock and performance awards (in shares)	4	3	5	4
Average shares outstanding - diluted (in shares)	434	439	437	440