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Income Taxes - Additional Information (Detail)
₨ / shares in Units, ₨ in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2018
INR (₨)
₨ / shares
Mar. 31, 2017
INR (₨)
₨ / shares
Mar. 31, 2016
INR (₨)
₨ / shares
Mar. 31, 2018
USD ($)
Disclosure of income tax expense [line items]        
Reversal of provisions pertaining to earlier periods ₨ 380 ₨ 593 ₨ 1,337  
Deferred tax asset of unused tax losses not recognized 3,756 4,238    
Tax loss carry-forwards 14,510 13,581    
Tax loss carry-forwards not currently subject to expiration dates 6,223 5,371    
Tax loss carry-forwards expires in various years ₨ 8,287 8,210    
Tax loss carry-forwards expiration period 2037      
Deferred tax asset of unused tax losses recognized ₨ 6,908 3,098   $ 106
Minimum alternate tax 74 1,520    
Decrease of current tax expense due to tax holidays ₨ 11,635 ₨ 11,958 ₨ 12,754  
Tax incentives per share | ₨ / shares ₨ 2.45 ₨ 2.46 ₨ 2.60  
Deferred tax liabilities on cumulative earnings of subsidiaries ₨ 51,432 ₨ 46,905    
Branch profit tax percentage 15.00%      
Unused tax losses [member]        
Disclosure of income tax expense [line items]        
Deferred tax asset of unused tax losses recognized ₨ 5,287 ₨ 5,513