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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, 2018
Mar. 31, 2017
Disclosure of actuarial assumptions [line items]    
Discount rate 6.30% 5.91%
Expected return on plan assets 6.30% 5.91%
Expected rate of salary increase 6.89% 6.90%
Duration of defined benefit obligations 8 8
Provident fund [member]    
Disclosure of actuarial assumptions [line items]    
Discount rate 7.35% 6.90%
Average remaining tenure of investment portfolio 7 years 6 years
Guaranteed rate of return 8.55% 8.65%