Pension and Other Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Oct. 26, 2018
Defined Benefit Plan Disclosure [Line Items]
Prior service cost				$ 28
Vesting period	1 year
Defined contribution plan contribution	$ 219	$ 245	$ 124
Shares of company common stock held in defined contribution plan assets	3,737,298
Deferred compensation plan, liability	$ 59	65
Deferred compensation plan, expense	2	4	5
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Gain due to remeasurement	17
Gain due to curtailment	40
Actuarial loss	23
Contractual termination benefits	3	$ 13	$ 1
Estimated future amortization of prior service credit	$ (9)
Non-employee directors
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation plan, maximum deferral percentage	100.00%