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Income Taxes - Summary of Reconciliation of Income Tax Expense (Detail)
₨ in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2018
INR (₨)
Mar. 31, 2018
USD ($)
Mar. 31, 2017
INR (₨)
Mar. 31, 2016
INR (₨)
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]        
Profit before taxes ₨ 102,474 $ 1,574 ₨ 110,356 ₨ 114,933
Enacted income tax rate in India 34.61% 34.61% 34.61% 34.61%
Computed expected tax expense ₨ 35,466   ₨ 38,194 ₨ 39,778
Income exempt from tax (12,878)   (12,684) (12,799)
Basis differences that will reverse during a tax holiday period 167   (274) (568)
Income taxed at higher/ (lower) rates (111)   (1,105) (1,449)
Reversal of deferred tax for past years due to rate reduction * (1,563)      
Taxes related to prior years (380)   (593) (1,337)
Changes in unrecognized deferred tax assets 239   40 87
Expenses disallowed for tax purpose 1,431   1,787 1,752
Others, net 19   (152) (98)
Income tax expense ₨ 22,390 $ 344 ₨ 25,213 ₨ 25,366
Effective income tax rate 21.85% 21.85% 22.85% 22.07%