Pension and Other Benefit Plans - Pension Plan, Net Periodic Costs and Other Changes (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 23	$ 23	$ 45	$ 46
Interest cost	61	57	119	117
Expected return on assets	(161)	(154)	(314)	(315)
Amortization of prior service costs	(2)	(2)	(4)	(4)
Contractual termination benefit	3	6	3	17
Curtailment gain	0	0	(9)	0
Recognition of actuarial loss	0	0	11	0
Net periodic pension income	$ (76)	$ (70)	$ (149)	$ (139)