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Mining and Income Taxation - Summary of Estimated Available for Set-off Against Future Income Pre Tax (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2014
South African Revenue Service [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Gross recognised capital allowance disallowed     $ 182.2
GFI Joint Venture Holdings (Proprietary) Limited [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Gross recognised capital allowance $ 925.5 $ 796.6  
Gross unrecognised capital allowance 1,501.6 1,132.6  
Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses $ 445.9 $ 388.8  
Abosso Goldfields Limited [member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Tax losses carry forward period Five Years Five Years  
Tax Losses Expiring Between 1 and 2 Years [Member] | Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses $ 22.9 $ 10.9  
Tax Losses Expiring Between 2 and 5 Years [Member] | Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses 57.6 58.9  
Tax Losses Expiring Between 5 and 10 Years [Member] | Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses 30.4 41.2  
Tax Losses Expiring After 10 Years [Member] | Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses 43.2 40.6  
No Expiry Date [Member] | Exploration Entities [Member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Total tax losses 291.8 237.2  
Tax Losses Expire in 2 Years [Member] | Abosso Goldfields Limited [member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Tax losses 44.5 46.3  
Tax Losses Expire in 3 Years [Member] | Abosso Goldfields Limited [member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Tax losses expiration value 19.0 0.0  
Tax Losses Expire in 4 Years [Member] | Abosso Goldfields Limited [member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Tax losses expiration value 91.7 19.4  
Tax Losses Expire in 5 Years [Member] | Abosso Goldfields Limited [member]      
Disclosure of Estimated Amount Available for Set Off Against Future Income Pretax [Line Items]      
Tax losses expiration value $ 46.2 $ 3.0