Employee Benefit Plans (Narratives) (Details) - USD ($)	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Compensation of related costs, Share-based Payments [Abstract]
Employee stock ownership plan (ESOP), compensation expense	$ 23,000,000.0	$ 10,300,000	$ 11,300,000
Employee stock ownership plan (ESOP), cash contributions to ESOP	5,600,000	1,000,000.0
Cash contributions to ESOP non leveraged	23,000,000.0	$ 4,000,000.0	$ 5,200,000
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	5.00%	6.90%
Defined benefit plan, ultimate health care cost trend rate	4.00%	4.50%
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