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	3 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020	Sep. 30, 2020 ZAR (R)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 ZAR (R)
Net adjusted external debt	$ 900.0		R 15.1	$ 900.0	R 15.8
Lease liabilities included in net adjusted external debt			4.2		4.4
Deferred tax including assessed tax losses	$ 172.3		R 2.9	$ 167.3	R 2.9
Weighted Average Cost of Capital (WACC) Rate [Member] \| Minimum [Member]
Investment fair value measurement inputs	16.00%	16.00%
Weighted Average Cost of Capital (WACC) Rate [Member] \| Maximum [Member]
Investment fair value measurement inputs	21.00%	21.00%
Long Term Growth Rate [Member]
Investment fair value measurement inputs	3.00%	3.00%
Marketability Discount [Member]
Investment fair value measurement inputs	10.00%
Minority Discount [Member]
Investment fair value measurement inputs	15.00%