Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	$ 11,725	$ 13,837
Current-period other comprehensive income (loss)	(104)	(375)
Amounts reclassified from accumulated other comprehensive income (loss)	(3)	5
Balance	11,217	11,814
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(517)	(261)
Current-period other comprehensive income (loss)	(111)	(342)
Amounts reclassified from accumulated other comprehensive income (loss)	0	6
Balance	(628)	(597)
Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(3)	9
Current-period other comprehensive income (loss)	6	(32)
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	0
Balance	1	(23)
Available-for-sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	9	9
Current-period other comprehensive income (loss)	1	(1)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Balance	10	8
Pension and Other Post-retirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	267	301
Current-period other comprehensive income (loss)	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(1)
Balance	266	300
Accumulated Other Comprehensive (Loss) Income
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Balance	(244)	58
Balance	$ (351)	$ (312)