Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 10,078	$ 9,338
Accumulated Amortization	4,347	3,399
Net Carrying Value	5,731	5,939
Software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,048	3,864
Accumulated Amortization	2,614	2,235
Net Carrying Value	1,434	1,629
Customer related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	5,795	5,389
Accumulated Amortization	1,697	1,139
Net Carrying Value	4,098	4,250
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	235	85
Accumulated Amortization	36	25
Net Carrying Value	$ 199	$ 60