Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	$ 5,129	$ 11,725
Current-period other comprehensive income (loss)	45	(180)
Amounts reclassified from accumulated other comprehensive loss	(4)	(4)
Balance	4,751	8,870
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(851)	(517)
Current-period other comprehensive income (loss)	28	(184)
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance	(823)	(701)
Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(20)	(3)
Current-period other comprehensive income (loss)	12	2
Amounts reclassified from accumulated other comprehensive loss	6	0
Balance	(2)	(1)
Available-for-sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	9	9
Current-period other comprehensive income (loss)	5	2
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance	14	11
Pension and Other Post-retirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	259	267
Current-period other comprehensive income (loss)	0	0
Amounts reclassified from accumulated other comprehensive loss	(10)	(4)
Balance	249	263
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(603)	(244)
Balance	$ (562)	$ (428)