Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Land and rights-of-way	$ 132.3	$ 115.7
Buildings and leasehold improvements	184.8	323.8
Network equipment	1,498.6	4,180.0
Office software, furniture, fixtures and vehicles	89.6	243.7
Construction in process	73.4	60.4
Gross value	1,978.7	4,923.6
Accumulated depreciation	(21.8)	(3,194.5)
Property, plant and equipment, net	$ 1,956.9	$ 1,729.1
Land [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Land [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	Indefinite
Building and Building Improvements [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Building and Building Improvements [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Equipment [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Equipment [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Furniture and Fixtures [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Furniture and Fixtures [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, Plant and Equipment, Useful Life	14 years