Receivables (Details) $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) agreement	Dec. 31, 2019 USD ($)
Schedule Of Financial Receivables [Line Items]
Accounts receivable securitization arrangements | agreement				2
Deferred purchase program receivable				$ 53	$ 246
Net cash funding received during the period				153
Amount of cash draws under arrangement during the period				189
Amount of cash repayments under arrangement during the period				342
Customer One
Schedule Of Financial Receivables [Line Items]
Accounts receivables sold	$ 8			32
Customer Two
Schedule Of Financial Receivables [Line Items]
Accounts receivables sold	34			99
Arconic Corporation
Schedule Of Financial Receivables [Line Items]
Deferred purchase program receivable			$ 282
Special purpose entity
Schedule Of Financial Receivables [Line Items]
Accounts receivables sold		$ 46		123
Receivables, maximum allowable purchase limit				125
Financing receivables, held as collateral	$ 28			$ 28
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold, maximum			$ 300		$ 400