Acquisitions - Narrative (Details) $ in Millions				12 Months Ended
	Jan. 01, 2021 USD ($)	Jun. 14, 2019 USD ($)	Oct. 01, 2018 USD ($)	Mar. 31, 2020 USD ($) acquisition	Mar. 31, 2021 USD ($)	Mar. 31, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill acquired				$ 2,017	$ 641	$ 7,606
Goodwill				2,017	$ 641	$ 7,606
AXA Bank Germany
Business Acquisition [Line Items]
Total consideration	$ 101
Cash received in acquisition	294
Customer deposit liabilities acquired	197
Goodwill acquired	2
Goodwill	$ 2
Luxoft
Business Acquisition [Line Items]
Total consideration		$ 2,000
Cash received in acquisition		113
Goodwill acquired		$ 1,262
Percentage of business acquired		100.00%
Current assets acquired		$ 361
Other assets		99
Other liabilities		72
Goodwill		$ 1,262
Molina Medicaid Solutions
Business Acquisition [Line Items]
Total consideration			$ 233
Goodwill acquired			92
Current assets acquired			87
Intangible assets, other than goodwill			112
Other assets			11
Current liabilities			51
Other liabilities			18
Goodwill			$ 92
Useful lives (years)			13 years
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Total consideration				228
Goodwill acquired				137
Current assets acquired				73
Intangible assets, other than goodwill				71
Other assets				10
Current liabilities				63
Goodwill				$ 137
Number of businesses acquired | acquisition				7
Payments to acquire businesses				$ 187
Contingent consideration				$ 41