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, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 EUR (€)	Sep. 30, 2020 GBP (£)	Mar. 31, 2020 EUR (€)	Sep. 30, 2019 EUR (€)	Sep. 30, 2019 GBP (£)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	$ 13	$ (23)	$ 40	$ 41
Reclassified to income statement, net of income tax expense	0	79	2	92
Other comprehensive income (loss)	13	56	42	133
Foreign currency translation adjustments, tax	0	0	0	0
Reclassified to income statement, tax	0	0	0	0
Unrealized gains (loss) on cash flow hedges arising during period, tax	4	(4)	4	(10)
Net actuarial loss and prior service cost arising during the period, tax	0	2	0	1
Amortization of actuarial (gain) loss and prior service costs, tax	(1)	0	(1)	0
Foreign currency translation adjustments and other, tax	0	0	0	0
Net actuarial gain (losses) attributable to redeemable noncontrolling interest	(5)	1	(2)	1
Foreign Currency Translation Adjustments, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	111	(114)	207	(44)
Reclassified to income statement, net of income tax expense	0	0	0	0
Other comprehensive income (loss)	111	(114)	207	(44)
Translation gain (loss) attributable to redeemable noncontrolling interest	(119)	(19)	(61)	(13)
Unrealized Gains on Net Investment Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(70)	82	(133)	56
Reclassified to income statement, net of income tax expense	0	0	0	0
Other comprehensive income (loss)	(70)	82	(133)	56
Unrealized gains (losses) on net investment hedges arising during period, tax	25	(29)	47	(20)
Reclassified to income statement, tax	0	0	0	0
Gain (loss) from net investment hedges recorded within other comprehensive income	(1)		(1)
Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(19)	13	(24)	25
Reclassified to income statement, net of income tax expense	0	0	0	0
Other comprehensive income (loss)	(19)	13	(24)	25
Reclassified to income statement, tax	0	0	0	0
Net actuarial gain and prior service cost arising during the period, net of income tax benefit of nil, $2, nil, and $1
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	0	(9)	0	(3)
Amortization of actuarial loss, prior service cost and transition obligation, net of income tax expense
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	0	1	2	2
Foreign currency translation adjustments and other, net of income tax expense of nil, nil, nil, and nil
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(9)	5	(10)	7
Changes in retirement-related benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified to income statement, net of income tax expense	0	78	0	90
Other comprehensive income (loss)	(9)	75	(8)	96
Reclassified to income statement, tax	0	27	0	32
Euro Denominated Notes | Term Loan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Long-term debt outstanding | €								€ 1,950
British Pound Sterling Denominated Notes | Term Loan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Long-term debt outstanding | £						£ 450			£ 450
Net Investment Hedging | Euro Denominated Notes | Term Loan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Long-term debt outstanding | €					€ 1,700		€ 1,700
Derivatives designated for hedge accounting
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain (loss) from net investment hedges recorded within other comprehensive income	(83)	91	(117)	67
Derivatives designated for hedge accounting | Net Investment Hedging
Accumulated Other Comprehensive Income (Loss) [Line Items]
Derivatives used in net investment hedge, gains (loss) gross	$ (12)	$ 20	$ (63)	$ 9