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Employee Benefits - Summary of Principal Assumptions Used for Purpose of Actuarial Valuation of Defined Benefit Plans (Detail) - yr
12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Disclosure of actuarial assumptions [line items]    
Discount rate 6.05% 6.30%
Expected return on plan assets 6.05% 6.30%
Expected rate of salary increase 6.80% 6.89%
Duration of defined benefit obligations 0 0
Provident fund [member]    
Disclosure of actuarial assumptions [line items]    
Discount rate 7.00% 7.35%
Average remaining tenure of investment portfolio 8 years 7 years
Guaranteed rate of return 8.65% 8.55%