Property, Plant and Equipment (Components of Property Plant and Equipment, Specifically Leased Devices) (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2017	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Document Period End Date	Sep. 30, 2017
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ (16,135)	$ (14,503)
Property, plant and equipment, net	18,901	19,209
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	8,214	7,276
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(3,505)	(3,114)
Property, plant and equipment, net	$ 4,709	$ 4,162