Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	[1]	Preferred Class A	Preferred stock	Common stock	Additional capital	Retained earnings (Accumulated other comprehensive loss)	Retained earnings (Accumulated other comprehensive loss) Cumulative Effect, Period of Adoption, Adjustment		Retained earnings (Accumulated other comprehensive loss) Preferred Class A	Accumulated other comprehensive loss	Accumulated other comprehensive loss Cumulative Effect, Period of Adoption, Adjustment		Noncontrolling Interests
Beginning balance at Dec. 31, 2018	$ 5,569	$ 73			$ 55	$ 483	$ 8,319	$ (374)	$ 75	[1]		$ (2,926)	$ (2)	[1]	$ 12
Beginning balance (Accounting Standards Update 2014-09) at Dec. 31, 2018									$ 73
Beginning balance (Accounting Standards Update 2017-12) at Dec. 31, 2018													$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	161							161
Other comprehensive income (loss)	0
Cash dividends declared:
Preferred dividends declared, value				$ (2)							$ (2)
Common share, value	(55)							(55)
Stock-based compensation	41						41
Common stock issued: compensation plans	3					3
Repurchase and retirement of common stock	(1,100)					(52)	(1,048)
Other	4						2								2
Ending balance at Sep. 30, 2019	4,694				55	434	7,314	(195)				(2,928)			14
Beginning balance at Jun. 30, 2019	4,850				55	440	7,484	(272)				(2,869)			12
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	95							95
Other comprehensive income (loss)	(59)											(59)
Cash dividends declared:
Preferred dividends declared, value				(1)							(1)
Common share, value	(17)							(17)
Stock-based compensation	16						16
Common stock issued: compensation plans	6					1	5
Repurchase and retirement of common stock	(200)					(7)	(193)
Other	4						2								2
Ending balance at Sep. 30, 2019	4,694				55	434	7,314	(195)				(2,928)			14
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 (loss)	30											30
Cash dividends declared:
Preferred dividends declared, value				(2)							(2)
Common share, value	(8)							(8)
Stock-based compensation	35						35
Common stock issued: compensation plans	(8)					3	(11)
Repurchase and retirement of common stock	(51)					(2)	(49)
Distributions to Arconic Corp	(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 (loss)	61											61
Cash dividends declared:
Preferred dividends declared, value				$ (1)							$ (1)
Stock-based compensation	12						12
Common stock issued: compensation plans	(5)						(5)
Repurchase and retirement of common stock	(51)					(2)	(49)
Distributions to Arconic Corp	0						22					(22)
Ending balance at Sep. 30, 2020	$ 3,501				$ 55	$ 434	$ 4,683	$ 258				$ (1,929)			$ 0

[1] The Company entered into a sale leaseback arrangement in October 2018 for a cast house that is now part of Arconic Corporation, and due to continuing involvement, the gain on sale was deferred. In connection with the adoption of the new lease accounting standard on January 1, 2019, the arrangement no longer required that the gain be deferred. As such, the associated $73 deferred gain, net of tax was recognized as a cumulative effect of an accounting change within Accumulated deficit. Also, the Company adopted the new hedge accounting guidance on January 1, 2019. As a result, an adjustment of $2 was recognized as a cumulative effect of an accounting change within Accumulated deficit with an offset to Accumulated other comprehensive loss related to the elimination of a separate measurement of ineffectiveness for its cash flow hedges.