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Assumption used to Value Shares (Detail) (ZAR)
12 Months Ended
Dec. 31, 2012
Performance Shares
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Weighted average historical volatility (based on a statistical analysis of the share price on a weighted moving average basis for the expected term of the option) 36.40%
Expected term (months) 3 years
Historical dividend yield 1.60%
Weighted average fair value - Rand 162.14
Performance Shares | US Interest Rates
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Weighted average three year risk free interest rate 0.70%
Bonus Share
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Weighted average historical volatility (based on a statistical analysis of the share price on a weighted moving average basis for the expected term of the option) 29.40%
Historical dividend yield 2.70%
Marketability discount 1.60%
Weighted average fair value - Rand 115.61
Bonus Share | Minimum
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Expected term (months) 9 months
Bonus Share | Maximum
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Expected term (months) 18 months
Bonus Share | SA Interest Rates
 
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Weighted average three year risk free interest rate 5.50%