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Risk Management Activities - Summary of Effect of Change in Finance Expense on Group's Profit or Loss had LIBOR and Prime Differed as Indicated (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
ExchangeRates
Dec. 31, 2022
USD ($)
ExchangeRates
Dec. 31, 2021
ExchangeRates
Rand      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Closing exchange rate | ExchangeRates 18.30 17.02 15.94
Average exchange rate | ExchangeRates 18.45 16.37 14.79
Closing foreign exchange rate | Rand      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Closing exchange rate | ExchangeRates 18.30 17.02  
Sensitivity to BBSY interest rates | Closing foreign exchange rate      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Average exchange rate | ExchangeRates 0.68 0.69  
-0.1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
(Decrease)/increase in OCI $ (6.6) $ (3.5)  
-0.05      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
(Decrease)/increase in OCI (3.3) (1.7)  
Increase/(decrease) in OCI 6.3 10.1  
0.05      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
(Decrease)/increase in OCI 3.3 1.7  
Increase/(decrease) in OCI (5.5) (8.0)  
0.1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
(Decrease)/increase in OCI 6.6 3.5  
-0.025      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in OCI 3.0 4.7  
0.025      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in OCI (2.8) (4.2)  
-0.01      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in equity accounted investee 3.3    
-0.01 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (2.0) (1.6)  
-0.01 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (1.2) (0.8)  
-0.01 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (0.8) (0.8)  
0.01      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in equity accounted investee (2.8)    
0.01 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 2.0 1.6  
0.01 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 1.2 0.8  
0.01 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 0.8 0.8  
1 year earlier      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in OCI 10.8 10.3  
1 year later      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in OCI (16.5) (10.9)  
6 months earlier      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in equity accounted investee 0.0    
6 months later      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Increase/(decrease) in equity accounted investee (6.7)    
-0.015 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (2.9) (2.5)  
-0.015 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (1.7) (1.3)  
-0.015 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (1.2) (1.2)  
-0.005 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (1.0) (0.8)  
-0.005 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (0.6) (0.4)  
-0.005 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense (0.4) (0.4)  
0.005 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 1.0 0.8  
0.005 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 0.6 0.4  
0.005 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 0.4 0.4  
0.015 | Sensitivity to interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 2.9 2.5  
0.015 | Sensitivity to interest rates | Sensitivity to LIBOR/SOFR/CDOR interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense 1.7 1.3  
0.015 | Sensitivity to interest rates | Sensitivity to BBSY interest rates      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Change in finance expense $ 1.2 $ 1.2