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
Balance at beginning of period at Dec. 31, 2018	$ 5,585	$ 73			$ 55	$ 483	$ 8,319	$ (358)	$ 75	[1]		$ (2,926)	$ (2)	[1]	$ 12
Balance at beginning of period (Accounting Standards Update 2014-09) at Dec. 31, 2018									$ 73
Balance at beginning of period (Accounting Standards Update 2017-12) at Dec. 31, 2018													$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	66							66
Other comprehensive income (loss)	59											59
Cash dividends declared:
Preferred dividends declared, value				$ (1)							$ (1)
Common share, value	(38)							(38)
Stock-based compensation	25						25
Common stock issued: compensation plans	(3)					2	(5)
Repurchase and retirement of common stock	(900)					(45)	(855)
Balance at end of period at Jun. 30, 2019	4,866				55	440	7,484	(256)				(2,869)			12
Balance at beginning of period at Mar. 31, 2019	5,178				55	453	7,644	(134)				(2,852)			12
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(121)							(121)
Other comprehensive income (loss)	(17)											(17)
Cash dividends declared:
Stock-based compensation	17						17
Common stock issued: compensation plans	10						10
Repurchase and retirement of common stock	(200)					(13)	(187)
Other	(1)							(1)
Balance at end of period at Jun. 30, 2019	4,866				55	440	7,484	(256)				(2,869)			12
Balance at beginning of period at Dec. 31, 2019	4,621				55	433	7,319	129				(3,329)			14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	119							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 (B)	(1,255)						(2,633)					1,392			(14)
Other	(16)							(16)
Balance at end of period at Jun. 30, 2020	3,449				55	436	4,703	223				(1,968)			0
Balance at beginning of period at Mar. 31, 2020	4,797				55	436	7,326	335				(3,369)			14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(96)							(96)
Other comprehensive income (loss)	9											9
Cash dividends declared:
Stock-based compensation	10						10
Distributions to Arconic Corp (B)							(2,633)					1,392			(14)
Other	(16)							(16)
Balance at end of period at Jun. 30, 2020	$ 3,449				$ 55	$ 436	$ 4,703	$ 223				$ (1,968)			$ 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.