Basis of Presentation (Narrative) (Details)	9 Months Ended
	Sep. 30, 2021	Jun. 01, 2021
Telenet
Schedule of Equity Method Investments [Line Items]
Percentage ownership in subsidiary	60.70%
VodafoneZiggo JV
Schedule of Equity Method Investments [Line Items]
Ownership percentage	50.00%
Co-venturer ownership percentage	50.00%
Telefonica
Schedule of Equity Method Investments [Line Items]
Co-venturer ownership percentage	50.00%
VMED O2 JV
Schedule of Equity Method Investments [Line Items]
Ownership percentage	50.00%	50.00%
Co-venturer ownership percentage		50.00%