Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 10,209	$ 9,338
Accumulated Amortization	3,916	3,399
Net Carrying Value	6,293	5,939
Software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,195	3,864
Accumulated Amortization	2,438	2,235
Net Carrying Value	1,757	1,629
Customer related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	5,759	5,389
Accumulated Amortization	1,445	1,139
Net Carrying Value	4,314	4,250
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	255	85
Accumulated Amortization	33	25
Net Carrying Value	$ 222	$ 60