Stockholders' Equity - Schedule of Other Comprehensive Income (Loss), Net of Tax (Details) € in Millions, £ in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 EUR (€)	Sep. 30, 2019 GBP (£)	Mar. 31, 2019 USD ($)	Mar. 31, 2019 EUR (€)	Mar. 31, 2019 GBP (£)	Sep. 30, 2018 EUR (€)	Sep. 30, 2018 GBP (£)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	$ (23)	$ 29	$ 41	$ (93)
Reclassified to income statement, net of income tax expense	79	3	92	4
Other Comprehensive Income (Loss), Net of Tax	56	32	133	(89)
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	(4)	0	(10)	0
Net actuarial loss and prior service cost arising during the period, tax	2	0	1	0
Amortization of actuarial loss and prior service costs, tax	0	2	0	2
Foreign currency translation adjustments and other, tax	0	0	0	0
Long-term debt outstanding	7,644		7,644				$ 7,595
Net actuarial gain (losses) attributable to redeemable noncontrolling interest	1	0		2
Foreign Currency Translation Adjustments, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(114)	5	(44)	(268)
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	(114)	5	(44)	(268)
Translation gain (loss) attributable to redeemable noncontrolling interest	(19)	(7)	(13)	(46)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	82	21	56	165
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	82	21	56	165
Unrealized gains (losses) on net investment hedges arising during period, tax	29	7	20	58
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	13	2	25	2
Reclassified to income statement, net of income tax expense	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	13	2	25	2
Reclassified to income statement, tax	0	0	0	0
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	(9)	0	(3)	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	1	3	2	4
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	5	1	7	8
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified to income statement, net of income tax expense	78	0	90	0
Other Comprehensive Income (Loss), Net of Tax	75	4	96	12
Reclassified to income statement, tax	(27)	0	(32)	0
Euro Denominated Notes | Term Loan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Long-term debt outstanding | €					€ 1,950			€ 1,950		€ 1,950
British Pound Sterling Denominated Notes | Term Loan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Long-term debt outstanding | £						£ 450			£ 450		£ 450
Derivatives designated for hedge accounting
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain (loss) from net investment hedges recorded in earnings	91	23	67	184
Derivatives designated for hedge accounting | Net Investment Hedging
Accumulated Other Comprehensive Income (Loss) [Line Items]
Derivatives used in net investment hedge, gains (loss) gross	$ 20	$ 5	$ 9	$ 39