Employee Benefit Plans (Narratives) (Details) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Compensation of related costs, Share-based Payments [Abstract]
Employee stock ownership plan (ESOP), compensation expense	$ 10,300,000	$ 11,300,000	$ 11,400,000
Employee stock ownership plan (ESOP), cash contributions to ESOP	5,600,000	1,000,000.0	1,000,000.0
Cash contributions to ESOP non leveraged	4,000,000.0	$ 5,200,000	$ 11,000,000.0
Unallocated common stock dividend, debt repayment	$ 0.0
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Defined benefit plan, health care cost trend rate assumed for next fiscal year	6.50%	6.90%
Defined benefit plan, ultimate health care cost trend rate	4.50%	4.50%
Defined benefit plan, effect of one percentage point increase on accumulated postretirement benefit obligation	$ 246
Defined benefit plan, effect of one percentage point increase on service and interest cost components	25
Defined benefit plan, effect of one percentage point decrease on accumulated postretirement benefit obligation	278
Defined benefit plan, effect of one percentage point decrease on service and interest cost components	29
Post retirement health insurance [Member]
Deferred Compensation Arrangements [Abstract]
Lifetime maximum benefit paid per individual	20,000
Post retirement life insurance [Member]
Deferred Compensation Arrangements [Abstract]
Lifetime maximum benefit paid per individual	3,000
Additional benefit requirement amount	$ 100