Segment Reporting (Revenue and Long-Lived Assets by Geographic Segments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenue	$ 2,949.1	$ 2,929.7	$ 3,015.6	$ 3,063.5	$ 2,987.8	$ 2,899.3	$ 2,746.8	$ 2,642.5	$ 11,957.9	$ 11,276.4	$ 13,731.1
VodafoneZiggo JV
Segment Reporting Information [Line Items]
Revenue											0.0
Revenue									4,602.2	4,512.5	0.0
Long-lived assets	22,026.2				24,017.4				22,026.2	24,017.4
Operating Segments
Segment Reporting Information [Line Items]
Revenue									11,957.9	11,276.4	13,731.1
Operating Segments | U.K.
Segment Reporting Information [Line Items]
Revenue									6,351.2	5,927.9	6,070.4
Operating Segments | Belgium
Segment Reporting Information [Line Items]
Revenue									2,993.6	2,865.3	2,691.1
Operating Segments | Switzerland
Segment Reporting Information [Line Items]
Revenue									1,326.0	1,370.1	1,377.4
Operating Segments | Ireland
Segment Reporting Information [Line Items]
Revenue									523.9	470.8	438.4
Operating Segments | Poland
Segment Reporting Information [Line Items]
Revenue									440.7	417.9	391.4
Operating Segments | Slovakia
Segment Reporting Information [Line Items]
Revenue									51.5	49.6	49.9
Operating Segments | The Netherlands
Segment Reporting Information [Line Items]
Revenue									0.0	0.0	2,690.8
Geography Eliminations
Segment Reporting Information [Line Items]
Revenue									271.0	174.8	$ 21.7
Total - continuing operations
Segment Reporting Information [Line Items]
Long-lived assets	28,629.0				30,114.7				28,629.0	30,114.7
Total - continuing operations | U.K.
Segment Reporting Information [Line Items]
Long-lived assets	15,489.2				16,902.9				15,489.2	16,902.9
Total - continuing operations | Belgium
Segment Reporting Information [Line Items]
Long-lived assets	5,979.4				6,067.9				5,979.4	6,067.9
Total - continuing operations | Switzerland
Segment Reporting Information [Line Items]
Long-lived assets	4,165.4				4,212.5				4,165.4	4,212.5
Total - continuing operations | Ireland
Segment Reporting Information [Line Items]
Long-lived assets	765.4				775.4				765.4	775.4
Total - continuing operations | Poland
Segment Reporting Information [Line Items]
Long-lived assets	958.7				1,028.4				958.7	1,028.4
Total - continuing operations | Slovakia
Segment Reporting Information [Line Items]
Long-lived assets	128.7				132.8				128.7	132.8
Total - continuing operations | U.S. and other
Segment Reporting Information [Line Items]
Long-lived assets	$ 1,142.2				$ 994.8				$ 1,142.2	$ 994.8