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Employee Benefit Plans - Healthcare Cost Trend Rates (Details) - Officer Medical Plan - Other Postretirement Benefits Plan
 12 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Defined Benefit Plan Disclosure [Line Items]    
Health care cost trend rate assumed for next year, Pre 65 6.60% 6.30%
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 6.80% 6.45%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate), Post 65 4.50% 4.50%