Property, Plant and Equipment (Components of Property Plant and Equipment) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	$ (20,539)	$ (17,423)
Property, plant and equipment, net	21,201	19,925
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	246	254
Network Equipment, Site Costs and Related Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	24,967	22,930
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	856	813
Non-network internal use software, office equipment, leased devices and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12,627	11,149
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Construction in progress	$ 3,044	$ 2,202

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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