Pension and Other Benefit Plans - Pension Plan, Amounts Recognized in Balance Sheet (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Other assets	$ 1,157	$ 1,118
Accrued expenses and other current liabilities	(20)	(28)
Non-current pension obligations	(790)	(879)
Other long-term liabilities - OPEB	(20)	(21)
Net amount recorded	327	190
Accumulated benefit obligation	$ 10,893	$ 11,241