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Schedule of Pension Plans Weighted-Average Asset Allocation and Range of Target Allocation (Detail)
12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
Percentage of Plan Assets at March 31 100.00% 100.00%
Equity Securities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Range of Target Allocation - Minimum 40.00%  
Range of Target Allocation - Maximum 60.00%  
Percentage of Plan Assets at March 31 70.00% 66.00%
Debt Securities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Range of Target Allocation - Minimum 35.00%  
Range of Target Allocation - Maximum 60.00%  
Percentage of Plan Assets at March 31 27.00% 33.00%
Other [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Range of Target Allocation - Minimum 0.00%  
Range of Target Allocation - Maximum 5.00%  
Percentage of Plan Assets at March 31 3.00% 1.00%