Revenue - Capitalized Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Capitalized sales commission cost
Capitalized Contract Cost [Line Items]
Capitalized contract cost, net	$ 256	$ 262
Capitalized contract cost, amortization	70	72	$ 62
Transition and transformation contract costs, net
Capitalized Contract Cost [Line Items]
Capitalized contract cost, net	888	874
Capitalized contract cost, amortization	$ 264	$ 280	$ 258