Effects on net income of amounts reclassified from accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (1)	$ (25)	$ (6)	$ (35)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(24)	(6)	(34)
Unrealized Gains (Losses) on Derivative Instruments [Member] | Sales Revenue, Net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(25)	(12)	(41)
Unrealized Gains (Losses) on Derivative Instruments [Member] | Research And Development [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 0	$ 1	$ 6	$ 7