Pension and Other Benefit Plans - Pension Plan, Amounts Recognized in Balance Sheet (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Other assets	$ 1,884	$ 1,735
Accrued expenses and other current liabilities	(81)	(16)
Non-current pension obligations	(796)	(761)
Other long-term liabilities - OPEB	(18)	(18)
Net amount recorded	989	940
Accumulated benefit obligation	$ 12,346	$ 10,072