Intangible Assets - Components of Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 290	$ 343	$ 929	$ 944
Intangible asset amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	224	272	735	747
Transition and transformation contract cost amortization
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 66	$ 71	$ 194	$ 197