Long-lived Assets (Schedule of PP&E) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 26,970.3	$ 26,587.4
Accumulated depreciation	(13,091.4)	(12,438.4)
Total property and equipment, net	13,878.9	14,149.0
Distribution systems
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	17,845.4	17,465.0
Customer premises equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	4,191.2	4,341.0
Support equipment, buildings and land
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 4,933.7	$ 4,781.4
Minimum | Distribution systems
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Minimum | Customer premises equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Minimum | Support equipment, buildings and land
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum | Distribution systems
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Maximum | Customer premises equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Maximum | Support equipment, buildings and land
Property, Plant and Equipment [Line Items]
Estimated useful life	50 years