Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Class A	Preferred stock	Common stock	Additional capital	Retained earnings	Retained earnings Class A	Accumulated other comprehensive loss	Noncontrolling interests
Beginning balance at Dec. 31, 2019	$ 4,605		$ 55	$ 433	$ 7,319	$ 113		$ (3,329)	$ 14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	119					119
Net income (loss)	119
Other comprehensive income (loss)	(31)							(31)
Cash dividends declared:
Preferred dividends declared, value		$ (1)					$ (1)
Common share, value	(8)					(8)
Stock-based compensation	23				23
Common stock issued: compensation plans	(3)			3	(6)
Distributions to Arconic Corp	(1,255)				(2,633)			1,392	(14)
Ending balance at Jun. 30, 2020	3,449		55	436	4,703	223		(1,968)	0
Beginning balance at Mar. 31, 2020	4,781		55	436	7,326	319		(3,369)	14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(96)					(96)
Net income (loss)	(96)
Other comprehensive income (loss)	9							9
Cash dividends declared:
Stock-based compensation	10				10
Distributions to Arconic Corp	(1,255)				(2,633)			1,392	(14)
Ending balance at Jun. 30, 2020	3,449		55	436	4,703	223		(1,968)	$ 0
Beginning balance at Dec. 31, 2020	3,577		55	433	4,668	364		(1,943)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	154					154
Other comprehensive income (loss)	59							59
Cash dividends declared:
Preferred dividends declared, value		$ (1)					$ (1)
Repurchase and retirement of common stock	(200)			(6)	(194)
Stock-based compensation	14				14
Common stock issued: compensation plans	(5)			2	(7)
Ending balance at Jun. 30, 2021	3,598		55	429	4,481	517		(1,884)
Beginning balance at Mar. 31, 2021	3,662		55	434	4,671	443		(1,941)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	74					74
Other comprehensive income (loss)	57							57
Cash dividends declared:
Repurchase and retirement of common stock	(200)			(6)	(194)
Stock-based compensation	8				8
Common stock issued: compensation plans	(3)			1	(4)
Ending balance at Jun. 30, 2021	$ 3,598		$ 55	$ 429	$ 4,481	$ 517		$ (1,884)