Pension and Other Benefit Plans - Pension Plan, Net Periodic Costs and Other Changes (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 23	$ 23	$ 68	$ 69
Interest cost	62	60	181	177
Expected return on assets	(163)	(161)	(477)	(476)
Amortization of prior service costs	(2)	(2)	(6)	(6)
Contractual termination benefit	0	0	3	17
Curtailment gain	0	0	(9)	0
Recognition of actuarial loss	0	0	11	0
Net periodic pension income	$ (80)	$ (80)	$ (229)	$ (219)