Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 8,465	$ 10,078
Accumulated Amortization	4,422	4,347
Net Carrying Value	4,043	5,731
Software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,014	4,048
Accumulated Amortization	2,733	2,614
Net Carrying Value	1,281	1,434
Customer related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,212	5,795
Accumulated Amortization	1,641	1,697
Net Carrying Value	2,571	4,098
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	239	235
Accumulated Amortization	48	36
Net Carrying Value	$ 191	$ 199