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Employee Benefits - Summary of Actuarial Assumptions (Detail)
12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Disclosure Of Defined Benefit Plans [Line Items]    
Withdrawal rate   25.00%
Bottom of Range [Member]    
Disclosure Of Defined Benefit Plans [Line Items]    
Discount rate (per annum) 5.40% 5.70%
Future salary growth (per annum) 5.00% 5.00%
Withdrawal rate 10.00%  
Retirement age (years) 58 years 58 years
Top of Range [Member]    
Disclosure Of Defined Benefit Plans [Line Items]    
Discount rate (per annum) 6.20% 6.40%
Future salary growth (per annum) 11.00% 11.00%
Withdrawal rate 25.00%  
Retirement age (years) 65 years 65 years