Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Weighted Average Actuarial Assumptions Used to Develop Projected Benefit Obligation (Detail)

v3.7.0.1
Employee Benefit Plans - Weighted Average Actuarial Assumptions Used to Develop Projected Benefit Obligation (Detail) - Other Postretirement Benefit Plans [Member]
12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 3.23% 3.16%
Medical care cost trend rate 8.00% 8.00%