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, 2020	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (64)	$ (7)	$ (1)
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	1	4
Unrealized Gains (Losses) on Available-for-Sale Securities | Interest Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	1	4
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(62)	(8)	5
Unrealized Gains (Losses) on Derivative Instruments | Sales Revenue, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(71)	(18)	10
Unrealized Gains (Losses) on Derivative Instruments | Research and Development
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	9	10	(5)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	(10)
Foreign Currency Translation Adjustment [Member] | Interest Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 0	$ 0	$ (10)