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, 2019	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	$ (7)	$ (1)	$ (37)
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	4	(1)
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	4	(1)
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	(8)	5	(36)
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	(18)	10	(37)
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	10	(5)	1
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	0	(10)	0
Foreign Currency Translation Adjustment [Member] | Interest Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	$ 0	$ (10)	$ 0