Fair Value Of Financial Instruments (Schedule Of Key Valuation Inputs Used To Measure Fair Value Of Investment In Cell C) (Details) - Cell C [Member] R in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Jun. 30, 2020	Dec. 31, 2020 ZAR (R)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 ZAR (R)
Net adjusted external debt	$ 800.0		R 11,200	$ 900.0	R 15,800
Lease liabilities included in net adjusted external debt			0		4,400
Deferred tax including assessed tax losses	$ 0.0		R 0	$ 167.3	R 2,900
Weighted Average Cost of Capital (WACC) Rate [Member] | Minimum [Member]
Investment fair value measurement inputs	17.00%	17.00%
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	3.00%	3.00%
Marketability Discount [Member]
Investment fair value measurement inputs	10.00%
Minority Discount [Member]
Investment fair value measurement inputs	15.00%