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Accounting Policies - Additional Information (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Disclosure of changes in accounting estimates [line items]        
Carrying amount of property, plant and equipment $ 4,892.9 $ 4,524.6 [1] $ 4,295.6 [1]  
Carrying value of goodwill 76.6 317.8 [1] 295.3  
Impairment loss 277.8 0.0 0.0  
Gold-in-process and stockpiles 305.4 234.3    
Provision for environmental rehabilitation costs 281.5 283.1 275.4  
Silicosis settlement costs 31.9 0.0    
Deferred taxation liability 453.9 458.6 [1] 482.2 [1]  
Deferred taxation asset 72.0 48.7 [1] 54.1  
Taxation payable 77.5 107.9 [1] 59.3 $ 37.8
Share-based payments 26.8 $ 14.0 [1] $ 10.7 [1]  
Increase in amortisation $ 5.7      
Dividends withholding tax percentage 20.00%      
Rand [member]        
Disclosure of changes in accounting estimates [line items]        
Closing exchange rate 12.58 14.03 15.10  
Average exchange rate 13.33 14.70 12.68  
US Dollars [member]        
Disclosure of changes in accounting estimates [line items]        
Closing exchange rate 0.77 0.72 0.73  
Average exchange rate 0.77 0.75 0.75  
Trade And Other Receivable [Member]        
Disclosure of changes in accounting estimates [line items]        
Derivative financial assets $ 25.0 $ 0.0    
Trade and Other Payable [Member]        
Disclosure of changes in accounting estimates [line items]        
Derivative financial liabilities $ 3.3 $ 0.0    
[1] As Restated - Refer note 40 for further details.