Arconic Inc. Separation Transaction and Discontinued Operations - Carrying Amount of Major Classes of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Total Assets of Discontinued Operations
Disposal Group, Including Discontinued Operation, Assets, Current, Total	$ 0	$ 1,442
Disposal Group, Including Discontinued Operation, Assets, Noncurrent, Total	0	3,899
Total Liabilities of Discontinued Operations:
Current liabilities of discontinued operations (B)	0	1,424
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent, Total	$ 0	2,258
Discontinued Operations, Disposed of by Means Other than Sale
Total Assets of Discontinued Operations
Cash and cash equivalents		71
Receivables from customers		385
Other receivables		135
Inventories		822
Prepaid expenses and other current assets		29
Disposal Group, Including Discontinued Operation, Assets, Current, Total		1,442
Properties, plants, and equipment, net		2,834
Goodwill		426
Intangibles, net		60
Deferred income taxes		383
Other noncurrent assets		196
Disposal Group, Including Discontinued Operation, Assets, Noncurrent, Total		3,899
Total assets of discontinued operations		5,341
Total Liabilities of Discontinued Operations:
Accounts payable, trade		1,067
Accrued compensation and retirement costs		147
Taxes, including income taxes		22
Other current liabilities		188
Current liabilities of discontinued operations (B)		1,424
Accrued pension benefits		1,430
Accrued other postretirement benefits		514
Other noncurrent liabilities and deferred credits		314
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent, Total		2,258
Total liabilities of discontinued operations		$ 3,682