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Financial instruments and risk management - Summary of derivative financial instruments (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Disclosure of detailed information about financial instruments [line items]    
Derivative assets $ 272 $ 665
Derivative financial liabilities (618) (184)
Disclosure Of Information About Amounts Recognised In Balance Sheet [Abstract]    
Non-current assets 210 531
Current assets 62 134
Current liabilities (225) (23)
Non-current liabilities (393) (161)
Total net derivative instruments (346) 481
Due within 1 year    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 62 134
Derivative financial liabilities (225) (23)
Between 1 and 5 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 60 330
Derivative financial liabilities (211) (14)
More than 5 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 150 201
Derivative financial liabilities (182) (147)
Other financial assets    
Disclosure of detailed information about financial instruments [line items]    
Total net derivative instruments 481
Derivatives designated as hedges    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 139 461
Derivative financial liabilities (365) (160)
Derivatives designated as hedges | Interest rate swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 139 386
Derivative financial liabilities (34) (1)
Derivatives designated as hedges | Cross currency interest rate swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 0 2
Derivative financial liabilities (206) (139)
Derivatives designated as hedges | Aluminium embedded derivatives    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 0 66
Derivative financial liabilities (125) (20)
Derivatives designated as hedges | Currency forward contracts    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 0 7
Derivative financial liabilities 0 0
Derivatives not designated as hedges    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 133 204
Derivative financial liabilities (253) (24)
Derivatives not designated as hedges | Aluminium embedded derivatives    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 53 80
Derivative financial liabilities (121) 0
Derivatives not designated as hedges | Currency forward contracts and swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 1 63
Derivative financial liabilities (39) (1)
Derivatives not designated as hedges | Other embedded derivatives    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 39 28
Derivative financial liabilities (1) (16)
Derivatives not designated as hedges | Other commodity contracts    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 40 33
Derivative financial liabilities $ (92) $ (7)