Supplemental Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Sales	$ 1,238	$ 1,134	$ 1,253	$ 1,634	$ 1,734	$ 1,794	$ 1,818	$ 1,752	$ 5,259	$ 7,098	$ 6,778
Net income from continuing operations attributable to common shareholders:	$ 106	$ 36	$ (84)	$ 153	$ 118	$ 58	$ (136)	$ 86	$ 211	$ 126	$ 309
Net income (loss) per share from continuing operations attributable to Howmet common shareholders
Net income (loss) from continuing operations - basic (in usd per share)	$ 0.24	$ 0.08	$ (0.19)	$ 0.35	$ 0.27	$ 0.13	$ (0.31)	$ 0.18	$ 0.48	$ 0.28	$ 0.64
Net income (loss) from continuing operations - diluted (in usd per share)	$ 0.24	$ 0.08	$ (0.19)	$ 0.34	$ 0.27	$ 0.13	$ (0.31)	$ 0.18	$ 0.48	$ 0.27	$ 0.63
Restructuring and other charges (E)									$ 182	$ 582	$ 163
U.K. Forging Business
Net income (loss) per share from continuing operations attributable to Howmet common shareholders
Restructuring and other charges (E)			$ 62
Financing
Net income (loss) per share from continuing operations attributable to Howmet common shareholders
Restructuring and other charges (E)			$ 59
Impairment Of Disks
Net income (loss) per share from continuing operations attributable to Howmet common shareholders
Restructuring and other charges (E)							$ 428			$ 428