Employee Benefit Plans - Weighted Average Discount Rate (Details) - Other Postretirement Benefits Plan	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Officer Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Weighted-average discount rate for benefit obligation	3.60%	4.10%	4.10%
Retired Officers' Bonus Plan
Defined Benefit Plan Disclosure [Line Items]
Weighted-average discount rate for benefit obligation	3.60%	4.10%	4.10%
Retired Vice Presidents' Bonus Plan
Defined Benefit Plan Disclosure [Line Items]
Weighted-average discount rate for benefit obligation	3.60%	4.10%	4.10%