Property, Plant and Equipment, Net - Components (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 3,301.2		$ 3,246.1
Less accumulated depreciation	(2,202.9)		(2,145.8)
Plant, Property and Equipment, Net	1,098.3		1,100.3
Depreciation expense	61.7	$ 55.4
Distribution facilities
Property, Plant and Equipment, Net
Total property, plant and equipment	1,999.3		1,960.0
Customer premise equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	488.1		481.5
Head-end equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	369.8		364.3
Telephony infrastructure
Property, Plant and Equipment, Net
Total property, plant and equipment	99.0		99.3
Computer equipment and software
Property, Plant and Equipment, Net
Total property, plant and equipment	169.2		163.9
Vehicles
Property, Plant and Equipment, Net
Total property, plant and equipment	34.6		35.9
Buildings and leasehold improvements
Property, Plant and Equipment, Net
Total property, plant and equipment	49.8		49.7
Office and technical equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	34.8		34.8
Land
Property, Plant and Equipment, Net
Total property, plant and equipment	6.2		6.2
Construction in progress (including material inventory and other)
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 50.4		$ 50.5