Employee Benefit Plans - Healthcare Cost Trend Rates (Details) - Officer Medical Plan - Other Postretirement Benefits Plan |
12 Months Ended | |
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Mar. 31, 2020 |
Mar. 31, 2019 |
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Defined Benefit Plan Disclosure [Line Items] | ||
Health care cost trend rate assumed for next year, Pre 65 | 6.80% | 7.50% |
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate), Pre 65 | 4.50% | 4.50% |
Health care cost trend rate assumed for next year, Post 65 | 7.00% | 7.75% |
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate), Post 65 | 4.50% | 4.50% |