Long-lived Assets (Schedule of PP&E) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 38,172.6	$ 36,235.0
Accumulated depreciation	(17,976.3)	(16,699.6)
Total property and equipment, net	20,196.3	19,535.4
Distribution Systems [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	26,482.9	25,202.2
Customer Premises Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,930.3	5,617.7
Support Equipment, Buildings and Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,759.4	$ 5,415.1