Intangible Assets - Components of Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 298	$ 287	$ 601	$ 569
Intangible asset amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	239	214	475	440
Transition and transformation contract cost amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 59	$ 73	$ 126	$ 129