Pension and Other Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 17	$ 32
Deferred compensation plan, liability	76	$ 76	$ 67
Non-employee directors
Defined Benefit Plan Disclosure [Line Items]
Maximum deferral percentage		100.00%
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions during remainder of Fiscal 2018	$ 38	$ 38