Pension and Other Benefit Plans - Pension Plan, Net Periodic Costs and Other Changes (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 22	$ 23
Interest cost	58	60
Expected return on assets	(153)	(161)
Amortization of prior service costs	(2)	(2)
Contractual termination benefit	0	11
Curtailment gain	(9)	0
Recognition of actuarial loss	11	0
Net periodic pension income	$ (73)	$ (69)