Long-lived Assets (Schedule of PP&E) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 15,744.5	$ 16,556.3
Accumulated depreciation	(8,192.4)	(8,502.2)
Total property and equipment, net	7,552.1	8,054.1
Distribution systems
Property, Plant and Equipment [Line Items]
Property and equipment gross	9,893.0	10,264.0
Customer premises equipment
Property, Plant and Equipment [Line Items]
Property and equipment gross	1,719.4	1,800.4
Support equipment, buildings and land
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 4,132.1	$ 4,491.9