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Fair Value Of Financial Instruments (Schedule Of Key Valuation Inputs Used To Measure Fair Value Of Investment In Cell C) (Details) - Cell C [Member]
$ in Millions, R in Billions
 9 Months Ended 12 Months Ended
Mar. 31, 2020
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2020
ZAR (R)
Jun. 30, 2019
ZAR (R)
Net adjusted external debt $ 1,000.0 $ 1,000.0 R 17.6 [1] R 13.9 [2]
Lease liabilities included in net adjusted external debt     5.8 [1] 6.4 [2]
Deferred tax including assessed tax losses $ 162.1 $ 205.9 R 2.9 R 2.9
Weighted Average Cost of Capital (WACC) Rate [Member] | Minimum [Member]        
Investment fair value measurement inputs 15.00% 15.00%    
Weighted Average Cost of Capital (WACC) Rate [Member] | Maximum [Member]        
Investment fair value measurement inputs 22.00% 22.00%    
Long Term Growth Rate [Member]        
Investment fair value measurement inputs 3.50% 4.50%    
Marketability Discount [Member]        
Investment fair value measurement inputs 10.00% 10.00%    
Minority Discount [Member]        
Investment fair value measurement inputs 15.00% 15.00%    
[1]
translated from ZAR to U.S. dollars at exchange rates applicable as of March 31, 2020.
[2]
translated from ZAR to U.S. dollars at exchange rates applicable as of June 30, 2019.