Segment Reporting (Narrative) (Details) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Jun. 30, 2018 |
Dec. 31, 2016 |
|
| Segment Reporting Information [Line Items] | |||
| Threshold percentage used to determine reportable segments using one of three criteria of revenue, operating cash flow or total assets | 10.00% | ||
| Performance measures, percentage of reportable segment revenue and operating cash flow presented | 100.00% | ||
| VodafoneZiggo JV | |||
| Segment Reporting Information [Line Items] | |||
| Percentage of minority interest revenues and expenses included in net earnings attributable to noncontrolling interest | 100.00% | ||
| Ownership percentage | 50.00% | 50.00% | 50.00% |
| Telenet | |||
| Segment Reporting Information [Line Items] | |||
| Percentage of minority interest revenues and expenses included in net earnings attributable to noncontrolling interest | 100.00% |