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Remeasurement Items affecting operating profit - Assumptions (Details)
 12 Months Ended
Jun. 30, 2018
R / $
$ / gal
$ / MMBTU
$ / bbl
Jun. 30, 2017
R / $
$ / gal
$ / MMBTU
$ / bbl
Jun. 30, 2016
R / $
$ / gal
$ / MMBTU
$ / bbl
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Long-term average crude oil price (in USD/bbl) | $ / bbl 73.91 74.29 85.37
Long-term average gas price (Henry Hub), excluding margins (real) (in USD/mmbtu) | $ / MMBTU 3.49 3.69 3.73
Long-term average ethane price (nominal) (in US$/gal) | $ / gal 0.3742 0.4427 0.6249
Long-term average exchange rate (R/US$) | R / $ 13.57 14.71 14.95
Future oil price period (in years) 5 years 5 years 10 years
Future exchange rate period (in years) 5 years 5 years 10 years
Future ethane price period (in years) 10 years 10 years  
Minimum      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Period over which management has projected cash flows 5 years    
South Africa      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Growth rate - long-term producer price index 5.50% 5.50% 6.02%
Weighted average cost of capital 12.71% 12.50% 14.05%
Discount rate - risk adjusted 12.71% 12.50% 14.05%
United States of America      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Growth rate - long-term producer price index 2.00% 2.00% 2.52%
Weighted average cost of capital 7.56% 6.60% 8.00%
Discount rate - risk adjusted 7.56% 6.60% 8.00%
Europe      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Growth rate - long-term producer price index 2.00% 2.00% 1.80%
Europe | Minimum      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Weighted average cost of capital 7.68% 6.60% 8.00%
Discount rate - risk adjusted 7.68% 6.60% 8.00%
Europe | Maximum      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Weighted average cost of capital 9.35% 8.22% 9.35%
Discount rate - risk adjusted 9.35% 8.22% 9.35%
Canada      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Growth rate - long-term producer price index 2.00% 2.00% 2.00%
Weighted average cost of capital 7.68% 6.60% 8.00%
Discount rate - risk adjusted 10.00%    
Canada | Minimum      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Discount rate - risk adjusted   9.50% 9.50%
Canada | Maximum      
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]      
Discount rate - risk adjusted   9.80% 9.80%