Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 3,117.6		$ 3,117.6		$ 3,013.7
Less accumulated depreciation	(2,041.1)		(2,041.1)		(1,940.0)
Plant, Property and Equipment, Net	1,076.5		1,076.5		1,073.7
Depreciation expense	56.5	$ 50.5	111.9	$ 99.7
Distribution facilities
Property, Plant and Equipment, Net
Total property, plant and equipment	1,882.5		1,882.5		1,780.7
Customer premise equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	470.3		470.3		460.1
Head-end equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	349.8		349.8		341.2
Telephony infrastructure
Property, Plant and Equipment, Net
Total property, plant and equipment	98.5		98.5		97.9
Computer equipment and software
Property, Plant and Equipment, Net
Total property, plant and equipment	153.9		153.9		146.4
Vehicles
Property, Plant and Equipment, Net
Total property, plant and equipment	34.3		34.3		37.0
Buildings and leasehold improvements
Property, Plant and Equipment, Net
Total property, plant and equipment	49.5		49.5		49.5
Office and technical equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	34.5		34.5		33.5
Land
Property, Plant and Equipment, Net
Total property, plant and equipment	6.2		6.2		6.2
Construction in progress (including material inventory and other)
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 38.1		$ 38.1		$ 61.2