Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 3,178.0		$ 3,178.0		$ 3,013.7
Less accumulated depreciation	(2,098.2)		(2,098.2)		(1,940.0)
Plant, Property and Equipment, Net	1,079.8		1,079.8		1,073.7
Depreciation expense	58.0	$ 50.4	169.9	$ 150.1
Distribution facilities
Property, Plant and Equipment, Net
Total property, plant and equipment	1,921.0		1,921.0		1,780.7
Customer premise equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	479.8		479.8		460.1
Head-end equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	354.4		354.4		341.2
Telephony infrastructure
Property, Plant and Equipment, Net
Total property, plant and equipment	98.8		98.8		97.9
Computer equipment and software
Property, Plant and Equipment, Net
Total property, plant and equipment	158.2		158.2		146.4
Vehicles
Property, Plant and Equipment, Net
Total property, plant and equipment	37.2		37.2		37.0
Buildings and leasehold improvements
Property, Plant and Equipment, Net
Total property, plant and equipment	49.6		49.6		49.5
Office and technical equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	34.7		34.7		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