Property, Plant and Equipment (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Years	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Land and rights-of-way	$ 117.2	$ 4.3
Buildings and leasehold improvements	305.2	179.1
Network equipment	3,913.3	3,339.4
Office software, furniture, fixtures and vehicles	216.3	162.5
Construction in process	47.1	14.7
Gross value	4,599.1	3,700.0
Accumulated depreciation	(2,755.1)	(2,571.0)
Property, plant and equipment, net	1,844.0	1,129.0
Depreciation	$ 239.6	$ 190.4	$ 182.0
Depreciation associated with cost of providing services	85.00%	84.00%	85.00%
Impairment of assets, excluding goodwill	$ 0.0	$ 0.0	$ 0.0
Capital Leased Assets, Gross	$ 114.9	$ 112.0
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life, Minimum in Practice | Years	7
Property, Plant and Equipment, Useful Life, Maximum in Practice | Years	25
Minimum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Minimum [Member] | Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Minimum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Maximum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Maximum [Member] | Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Maximum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	14 years