Pension and Other Benefit Plans - Pension Plan, Assumptions and Other Selected Information (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Benefit Plans with Projected Benefit Obligation in Excess of Plan Assets
Projected benefit obligation	$ 2,490	$ 2,191
Accumulated benefit obligation	2,431	2,131
Fair value of plan assets	1,596	1,397
Benefit Plans with Accumulated Benefit Obligation in Excess of Plan Assets
Projected benefit obligation	2,453	2,159
Accumulated benefit obligation	2,402	2,108
Fair value of plan assets	$ 1,562	$ 1,369

Amount of accumulated benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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