Financial Instruments and Risk Management - General (Details) $ / shares in Units, item in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) item approach $ / shares	Dec. 31, 2020 USD ($)
Financial Instruments and Risk Management
Aggregate fair value of derivative instruments with credit-risk-related contingent features that were in a net liability position	$ 7	$ 52
Collateral amount posted for derivative instruments with credit-risk-related contingent features that were in a net liability position	$ 0	$ 0
Commodity contracts
Financial Instruments and Risk Management
Number of methods through which entity manages commodity price risk in connection with market price fluctuations of aluminum ingot | approach	2
Notional amount of derivatives	$ 1,692
Gain (loss) on derivatives included in AOCI, net of tax	138
Net gain (loss) expected to be recognized in net earnings within the next 12 months	$ 130
Commodity contracts | Cash Flow Hedging
Financial Instruments and Risk Management
Period within which derivative will expire	3 years
Currency Exchange Rate Risk
Financial Instruments and Risk Management
Notional amount of derivatives	$ 2,803
Gain (loss) on derivatives included in AOCI, net of tax	27
Net gain (loss) expected to be recognized in net earnings within the next 12 months	$ 19
Currency Exchange Rate Risk | Cash Flow Hedging
Financial Instruments and Risk Management
Period within which derivative will expire	3 years
Interest rate swap and option contracts
Financial Instruments and Risk Management
Notional amount of derivatives	$ 1,795
Interest rate swap and option contracts | Cash Flow Hedging
Financial Instruments and Risk Management
Period within which derivative will expire	2 years
Equity contracts
Financial Instruments and Risk Management
Combined notional value, shares | item	2.6
Change in company's stock price (in dollars per share) | $ / shares	$ 1