Intangible Assets - Components of Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 325	$ 298	$ 639	$ 601
Intangible asset amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	258	239	511	475
Transition and transformation contract cost amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 67	$ 59	$ 128	$ 126