Pension and Other Benefit Plans - Pension Plan, Assumptions and Other Selected Information (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Benefit Plans with Projected Benefit Obligation in Excess of Plan Assets
Projected benefit obligation	$ 2,191	$ 2,329
Accumulated benefit obligation	2,131	2,230
Fair value of plan assets	1,397	1,494
Benefit Plans with Accumulated Benefit Obligation in Excess of Plan Assets
Projected benefit obligation	2,159	2,070
Accumulated benefit obligation	2,108	2,004
Fair value of plan assets	$ 1,369	$ 1,255