Accumulated Other Comprehensive Income Effects on net income of amounts reclassified from accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	$ (37)	$ (12)	$ 11
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(1)	0	0
Unrealized Gains (Losses) on Available-for-Sale Securities | Interest Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(1)	0	0
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(36)	(12)	11
Unrealized Gains (Losses) on Derivative Instruments | Sales Revenue, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(37)	(23)	(2)
Unrealized Gains (Losses) on Derivative Instruments | Research and Development
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	$ 1	$ 11	$ 13