Pension and Other Benefit Plans - Pension Plan, Reconciliation of Changes in PBO and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Assets assumed as a result of the HPES merger	$ 0	$ 7,411
Pension Plans, Defined Benefit
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	11,384	3,297
Benefit obligation assumed as a result of the HPES merger	0	7,351
Service cost	88	121	$ 23
Interest cost	253	249	82
Plan participants’ contributions	13	16
Amendments	27	(44)
Business/contract acquisitions/divestitures	0	69
Contractual termination benefits	3	13
Settlement/curtailment	(49)	(65)
Actuarial loss (gain)	286	(332)
Benefits paid	(344)	(447)
Foreign currency exchange rate changes	(818)	1,170
Other	173	(14)
Projected benefit obligation at end of year	$ 11,016	$ 11,384	3,297
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.40%	2.50%
Rates of increase in compensation levels	2.00%	2.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 11,574	$ 2,998
Actual return on plan assets	700	371
Employer contribution	78	83
Plan participants’ contributions	13	16
Benefits paid	(344)	(447)
Business/contract acquisitions/divestitures	0	(2)
Contractual termination benefits	17	4
Plan settlement	(38)	(22)
Foreign currency exchange rate changes	(837)	1,176
Other	180	(14)
Fair value of plan assets at end of year	11,343	11,574	$ 2,998
Funded status at end of year	$ 327	$ 190