Property, Plant and Equipment (Components of Property Plant and Equipment) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	$ (8,459)	$ (5,358)
Property, plant and equipment, net	20,645	19,721
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	266	266
Network equipment, site costs and related software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	21,304	18,990
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	793	754
Non-network internal use software, office equipment, leased devices and other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	5,346	2,979
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Construction in progress	$ 1,395	$ 2,090