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Activity in Options Available to be Granted Under Employee Stock Option Scheme (Detail) - Employees Stock Option Scheme - shares
12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options available to be granted, beginning of period 202,413,370 235,683,200 267,347,300
Equity shares allocated for grant under the plan 0 0 0
Options granted (47,773,600) (39,790,000) (33,764,100)
Forfeited/lapsed 4,847,580 6,520,170 2,100,000
Options available to be granted, end of period 159,487,350 202,413,370 235,683,200