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Intangible assets - Summary of intangible assets (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period $ 2,755 $ 2,637  
Adjustment on currency translation (48) 111  
Expenditure during the year 225 156  
Amortisation for the year (178) (161) $ (133)
Impairment charges   (4)  
Disposals, transfers and other movements 78 16  
Intangible assets at end of period 2,832 2,755 2,637
Cost      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 7,427    
Intangible assets at end of period 7,547 7,427  
Accumulated amortisation and impairment      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period (4,672)    
Intangible assets at end of period $ (4,715) $ (4,672)  
Quebec smelters      
Disclosure of detailed information about intangible assets [Line Items]      
Fair value less costs of disposal, post-tax discount rate 6.60% 6.60%  
Exploration and evaluation      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period $ 271 $ 173  
Adjustment on currency translation (14) 17  
Expenditure during the year 110 87  
Amortisation for the year 0 0  
Impairment charges   0  
Disposals, transfers and other movements (4) (6)  
Intangible assets at end of period 363 271 173
Exploration and evaluation | Cost      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 2,415    
Intangible assets at end of period 2,513 2,415  
Exploration and evaluation | Accumulated amortisation and impairment      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period (2,144)    
Intangible assets at end of period (2,150) (2,144)  
Trademarks, patented and non-patented technology      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 33 44  
Adjustment on currency translation (2) 3  
Expenditure during the year 5 0  
Amortisation for the year (14) (14)  
Impairment charges   0  
Disposals, transfers and other movements 0 0  
Intangible assets at end of period 22 33 44
Trademarks, patented and non-patented technology | Cost      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 232    
Intangible assets at end of period 220 232  
Trademarks, patented and non-patented technology | Accumulated amortisation and impairment      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period (199)    
Intangible assets at end of period (198) (199)  
Contract based intangible assets      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 1,994 1,947  
Adjustment on currency translation (11) 56  
Expenditure during the year 0 0  
Amortisation for the year (10) (8)  
Impairment charges   0  
Disposals, transfers and other movements 35 (1)  
Intangible assets at end of period 2,008 1,994 1,947
Contract based intangible assets | Cost      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 3,070    
Intangible assets at end of period 3,089 3,070  
Contract based intangible assets | Accumulated amortisation and impairment      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period (1,076)    
Intangible assets at end of period (1,081) (1,076)  
Other intangible assets      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 457 473  
Adjustment on currency translation (21) 35  
Expenditure during the year 110 69  
Amortisation for the year (154) (139)  
Impairment charges   (4)  
Disposals, transfers and other movements 47 23  
Intangible assets at end of period 439 457 $ 473
Other intangible assets | Cost      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 1,710    
Intangible assets at end of period 1,725 1,710  
Other intangible assets | Accumulated amortisation and impairment      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period (1,253)    
Intangible assets at end of period (1,286) (1,253)  
Water rights | Quebec smelters      
Disclosure of detailed information about intangible assets [Line Items]      
Intangible assets at beginning of period 1,798    
Intangible assets at end of period $ 1,796 $ 1,798  
Bottom of range | Other intangible assets      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 2 years    
Bottom of range | Trademarks      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 14 years    
Bottom of range | Patented and non-patented technology      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 10 years    
Bottom of range | Power contracts water rights      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 2 years    
Bottom of range | Other purchase and customer contracts      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 5 years    
Bottom of range | Computer software      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 2 years    
Top of range | Other intangible assets      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 20 years    
Top of range | Trademarks      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 20 years    
Top of range | Patented and non-patented technology      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 20 years    
Top of range | Power contracts water rights      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 45 years    
Top of range | Other purchase and customer contracts      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 15 years    
Top of range | Computer software      
Disclosure of detailed information about intangible assets [Line Items]      
Useful life measured as period of time, intangible assets other than goodwill 5 years