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	155					155
Other comprehensive income	30							30
Cash dividends declared:
Preferred dividends declared, value		$ (2)					$ (2)
Common share, value	(8)					(8)
Repurchase and retirement of common stock	(51)			(2)	(49)
Stock-based compensation	35				35
Common stock issued: compensation plans	(8)			3	(11)
Distributions to Arconic Corporation	(1,255)				(2,611)			1,370	(14)
Ending balance at Sep. 30, 2020	3,501		55	434	4,683	258		(1,929)	0
Beginning balance at Jun. 30, 2020	3,449		55	436	4,703	223		(1,968)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36					36
Other comprehensive income	61							61
Cash dividends declared:
Preferred dividends declared, value		(1)					(1)
Repurchase and retirement of common stock	(51)			(2)	(49)
Stock-based compensation	12				12
Common stock issued: compensation plans	(5)				(5)
Distributions to Arconic Corporation	0				22			(22)
Ending balance at Sep. 30, 2020	3,501		55	434	4,683	258		(1,929)	$ 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	181					181
Other comprehensive income	32							32
Cash dividends declared:
Preferred dividends declared, value		(2)					(2)
Common share, value	(9)					(9)
Repurchase and retirement of common stock	(225)			(7)	(218)
Stock-based compensation	28				28
Common stock issued: compensation plans	(3)			2	(5)
Ending balance at Sep. 30, 2021	3,579		55	428	4,473	534		(1,911)
Beginning balance at Jun. 30, 2021	3,598		55	429	4,481	517		(1,884)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27					27
Other comprehensive income	(27)							(27)
Cash dividends declared:
Preferred dividends declared, value		$ (1)					$ (1)
Common share, value	(9)					(9)
Repurchase and retirement of common stock	(25)			(1)	(24)
Stock-based compensation	14				14
Common stock issued: compensation plans	2				2
Ending balance at Sep. 30, 2021	$ 3,579		$ 55	$ 428	$ 4,473	$ 534		$ (1,911)