Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) - Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	$ 11,725	$ 13,837	$ 2,166
Current-period other comprehensive (loss) income	(349)	(299)	195
Amounts reclassified from accumulated other comprehensive (loss) income, net of taxes	(10)	(3)	25
Balance	5,129	11,725	13,837
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(517)	(261)	(458)
Current-period other comprehensive (loss) income	(334)	(256)	197
Amounts reclassified from accumulated other comprehensive (loss) income, net of taxes	0	0	0
Balance	(851)	(517)	(261)
Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(3)	9	20
Current-period other comprehensive (loss) income	(15)	(22)	(11)
Amounts reclassified from accumulated other comprehensive (loss) income, net of taxes	(2)	10	0
Balance	(20)	(3)	9
Available-for-sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	9	9	0
Current-period other comprehensive (loss) income	0	0	9
Amounts reclassified from accumulated other comprehensive (loss) income, net of taxes	0	0	0
Balance	9	9	9
Pension and other post-retirement benefit plans:
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	267	301	276
Current-period other comprehensive (loss) income	0	(21)	0
Amounts reclassified from accumulated other comprehensive (loss) income, net of taxes	(8)	(13)	25
Balance	259	267	301
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(244)	58	(162)
Balance	$ (603)	$ (244)	$ 58