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Risk Management Activities - Market Risk - Outstanding Hedges - Narrative (Detail)
$ in Millions, $ in Millions
 1 Months Ended 2 Months Ended 12 Months Ended
Mar. 31, 2020
$ / $
Jun. 30, 2019
l
$ / Boe
partsPerMillion
Jun. 30, 2017
l
partsPerMillion
$ / Boe
Dec. 31, 2021
AUD ($)
partsPerMillion
ExchangeRates
$ / Boe
l
Dec. 31, 2021
USD ($)
Dec. 31, 2020
AUD ($)
Dec. 31, 2020
USD ($)
Chile, Pesos              
Disclosure of Financial Risk Management [line items]              
Average strike rate 836.45     836.45      
Currency risk | Fair value hedges | Salares Norte              
Disclosure of Financial Risk Management [line items]              
Hedging instrument, liabilities | $         $ (6.8)    
Currency risk | Fair value hedges | – within one year | Salares Norte              
Disclosure of Financial Risk Management [line items]              
Nominal amount of hedging instrument | $         179.0    
Australia | Fair value hedges | Cash settled swap transaction contracts              
Disclosure of Financial Risk Management [line items]              
Hedging instrument, liabilities           $ (6.6) $ (5.1)
Australia | Commodity price risk | Cash settled swap transaction contracts | Brent crude              
Disclosure of Financial Risk Management [line items]              
Volume of diesel hedged | l       26,600,000      
Swap price per barrel hedged | $ / Boe       74.0      
Diesel sulphur measure | partsPerMillion       10      
Hedging instrument, liabilities       $ 2.7     2.0
Australia | Commodity price risk | Fair value hedges              
Disclosure of Financial Risk Management [line items]              
Hedging instrument, liabilities           $ (35.5) (27.3)
Australia | Commodity price risk | Fair value hedges | Cash settled swap transaction contracts              
Disclosure of Financial Risk Management [line items]              
Volume of diesel hedged | l   75,000,000 77,500,000        
Swap price per barrel hedged | $ / Boe   74.0 61.2        
Diesel sulphur measure | partsPerMillion   10 10        
Ghana | Fair value hedges | Cash settled swap transaction contracts              
Disclosure of Financial Risk Management [line items]              
Hedging instrument, liabilities | $         $ (3.1)   $ 10.0
Ghana | Commodity price risk | Cash settled swap transaction contracts | Brent crude              
Disclosure of Financial Risk Management [line items]              
Volume of diesel hedged | l       41,900,000      
Swap price per barrel hedged | $ / Boe       75.8      
Hedging instrument, liabilities | $         $ 3.1    
Ghana | Commodity price risk | Fair value hedges | Cash settled swap transaction contracts              
Disclosure of Financial Risk Management [line items]              
Volume of diesel hedged | l   123,200,000 125,800,000        
Swap price per barrel hedged | $ / Boe   75.8 61.4