Stockholders' Equity - Schedule of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($)	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	$ 29,000,000		$ (93,000,000)
Reclassified to income statement, net of income tax expense	3,000,000		4,000,000
Other Comprehensive Income (Loss), Net of Tax	32,000,000	$ 259,000,000	(89,000,000)	$ 580,000,000
Foreign currency translation adjustments arising during period, tax	0	0	0	0
Reclassified to income statement, tax	0	0	0	0
Unrealized gains on cash flow hedges arising during period, tax	0	0	0	0
Net actuarial loss and prior service cost arising during the period, tax	0	0	0	0
Amortization of actuarial loss and prior service costs, tax	2,000,000	0	2,000,000	0
Foreign currency translation adjustments and other, tax	0	0	0	0
Foreign Currency Translation Adjustments, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	5,000,000	303,000,000	(268,000,000)	685,000,000
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	5,000,000	303,000,000	(268,000,000)	685,000,000
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	21,000,000	(38,000,000)	165,000,000	(108,000,000)
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	21,000,000	(38,000,000)	165,000,000	(108,000,000)
Unrealized gains (losses) on net investment hedges arising during period, tax	(7,000,000)	25,000,000	(58,000,000)	69,000,000
Reclassified to income statement, tax	0	0	0	0
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	2,000,000	(3,000,000)	2,000,000	11,000,000
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	2,000,000	(3,000,000)	2,000,000	11,000,000
Accumulated Defined Benefit Plans Adjustment, Net Prior Service and Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	0	0	0	0
Accumulated Defined Benefit Plans Adjustment, Amortization of Actuarial Loss, Prior Service Cost and Transition Obligation, Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	3,000,000	1,000,000	4,000,000	2,000,000
Accumulated Defined Benefit Plans, Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	1,000,000	(4,000,000)	8,000,000	(10,000,000)
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	$ 4,000,000	$ (3,000,000)	$ 12,000,000	$ (8,000,000)

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