Pension and Other Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 12	$ 52
Prior service cost	28	28
Deferred compensation plan, liability	61	$ 61	$ 65
Non-employee directors
Defined Benefit Plan Disclosure [Line Items]
Maximum deferral percentage		100.00%
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions during remainder of Fiscal 2019	$ 30	$ 30