Pension and Other Benefit Plans - Pension Plan, Reconciliation of Changes in PBO and Fair Value of Plan Assets (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 10,150	$ 11,016
Service cost	91	92	$ 88
Interest cost	245	237	253
Plan participants’ contributions	31	30
Amendments	(9)	0
Business/contract acquisitions/divestitures	11	12
Contractual termination benefits	13	10
Settlement/curtailment	(37)	(60)
Actuarial loss (gain)	1,262	(362)
Benefits paid	(393)	(359)
Foreign currency exchange rate changes	1,084	(457)
Other	(12)	(9)
Projected benefit obligation at end of year	$ 12,436	$ 10,150	11,016
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.00%	2.40%
Rates of increase in compensation levels	2.50%	1.60%
Interest Crediting Rate	4.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 11,090	$ 11,343
Actual return on plan assets	1,401	526
Employer contribution	117	108
Plan participants’ contributions	31	30
Benefits paid	(393)	(359)
Business/contract acquisitions/divestitures	0	7
Contractual termination benefits	7	15
Plan settlement	(31)	(63)
Foreign currency exchange rate changes	1,224	(507)
Other	(21)	(10)
Fair value of plan assets at end of year	13,425	11,090	$ 11,343
Funded status at end of year	$ 989	$ 940