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	6 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 ZAR (R)	Jun. 30, 2019 ZAR (R)
Net adjusted external debt	$ 1,200.0	$ 1,000.0	R 16.4	R 13.9
Lease liabilities included in net adjusted external debt			6.0	6.4
Deferred tax including assessed tax losses	$ 206.4	$ 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	20.00%	20.00%
Long Term Growth Rate [Member]
Investment fair value measurement inputs	3.00%	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%