Property, Plant and Equipment (Components of Property Plant and Equipment, Specifically Leased Devices) (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2017	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Document Period End Date	Dec. 31, 2017
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ (16,727)	$ (14,503)
Property, plant and equipment, net	19,712	19,209
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	9,098	7,276
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(3,415)	(3,114)
Property, plant and equipment, net	$ 5,683	$ 4,162