Plant, Property and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Plant, Property and Equipment, Net
Total plant, property and equipment	$ 2,902.6		$ 2,902.6		$ 2,809.0
Less accumulated depreciation	(1,844.1)		(1,844.1)		(1,755.6)
Plant, Property and Equipment, Net	1,058.5		1,058.5		1,053.4
Depreciation expense	50.5	$ 45.9	99.7	$ 91.7
Distribution facilities
Plant, Property and Equipment, Net
Total plant, property and equipment	1,656.1		1,656.1		1,543.3
Customer premise equipment
Plant, Property and Equipment, Net
Total plant, property and equipment	445.9		445.9		440.4
Head-end equipment
Plant, Property and Equipment, Net
Total plant, property and equipment	332.3		332.3		321.9
Telephony infrastructure
Plant, Property and Equipment, Net
Total plant, property and equipment	97.5		97.5		94.8
Computer equipment and software
Plant, Property and Equipment, Net
Total plant, property and equipment	138.6		138.6		129.1
Vehicles
Plant, Property and Equipment, Net
Total plant, property and equipment	35.2		35.2		36.5
Buildings and leasehold improvements
Plant, Property and Equipment, Net
Total plant, property and equipment	47.2		47.2		46.3
Office and technical equipment
Plant, Property and Equipment, Net
Total plant, property and equipment	32.8		32.8		32.7
Land
Plant, Property and Equipment, Net
Total plant, property and equipment	6.2		6.2		6.2
Construction in progress (including material inventory and other)
Plant, Property and Equipment, Net
Total plant, property and equipment	$ 110.8		$ 110.8		$ 157.8