Property, Plant and Equipment (Components of Property Plant and Equipment, Specifically Leased Devices) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ (19,805)	$ (17,423)
Property, plant and equipment, net	21,422	19,925
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	10,987	9,592
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(4,304)	(3,580)
Property, plant and equipment, net	$ 6,683	$ 6,012