Commitments and Contingencies (Narrative) (Details) € in Millions, £ in Millions	1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 GBP (£)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 GBP (£)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 GBP (£)	Jul. 05, 2019	Jun. 30, 2019 GBP (£)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Aug. 01, 2018	Nov. 26, 2007 association
Loss Contingencies [Line Items]
Programming costs							$ 847,000,000.0	$ 784,300,000
Interkabel Acquisition
Loss Contingencies [Line Items]
Damages sought			€ 1,400.0	$ 1,600,000,000
Interkabel Acquisition
Loss Contingencies [Line Items]
Number of associations of municipalities in Belgium | association																		4
Loss contingency damages in excess value															€ 20.0	$ 22,700,000
Loss contingency accrual							$ 0
Deutsche Telekom Litigation
Loss Contingencies [Line Items]
Damages sought									€ 75.0	$ 85,000,000
Reduction of annual lease fees							83.33%
Belgium Regulatory Developments
Loss Contingencies [Line Items]
Percent of reduction in monthly wholesale cable resale access prices																	17.00%
Virgin Media VAT Matters
Loss Contingencies [Line Items]
Loss contingency accrual							$ 0
Virgin Media VAT Matters | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss							$ 60,000,000							£ 47.0
Virgin Media VAT Legislation Change
Loss Contingencies [Line Items]
Continuing operations					$ 99,100,000	£ 67.0
Provisions for litigation	$ 83,100,000	£ 63.7
Interest expense	$ 4,400,000	£ 3.3
Other Regulatory Issues | Maximum | Forecast | U.K.
Loss Contingencies [Line Items]
Estimate of possible loss											$ 39,000,000	£ 31.0
Subsequent Event | Belgium Regulatory Developments
Loss Contingencies [Line Items]
Percent of reduction in monthly wholesale cable resale access prices													25.00%