Long-lived Assets (Schedule of PP&E) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 14,962.7	$ 15,460.8
Accumulated depreciation	(7,978.1)	(7,834.2)
Total property and equipment, net	6,984.6	7,626.6
Distribution systems
Property, Plant and Equipment [Line Items]
Property and equipment gross	9,412.9	9,646.4
Customer premises equipment
Property, Plant and Equipment [Line Items]
Property and equipment gross	1,387.0	1,447.7
Support equipment, buildings and land
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 4,162.8	$ 4,366.7