Property, Plant and Equipment (Components of Property Plant and Equipment) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Document Period End Date	Jun. 30, 2018
Less accumulated depreciation	$ (18,418)	$ (17,423)
Property, plant and equipment, net	20,538	19,925
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	254	254
Network equipment, site costs and related software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	23,144	22,930
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	817	813
Non-network internal use software, office equipment, leased devices and other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	11,740	11,149
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Construction in progress	$ 3,001	$ 2,202