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Income Taxes - Additional Information (Detail)
₨ / shares in Units, ₨ in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2020
INR (₨)
₨ / shares
Mar. 31, 2019
INR (₨)
₨ / shares
Mar. 31, 2018
INR (₨)
₨ / shares
Mar. 31, 2020
USD ($)
Disclosure of income tax expense [line items]        
Deferred tax asset of unused tax losses not recognized ₨ 8,124 ₨ 6,769    
Tax loss carry-forwards 29,736 24,355    
Tax loss carry-forwards not currently subject to expiration dates 14,429 8,191    
Tax loss carry-forwards expires in various years ₨ 15,307 16,164    
Tax loss carry-forwards expiration period 2038      
Deferred tax asset of unused tax losses recognized ₨ 6,005 5,604   $ 80
Minimum alternate tax 3,425 0    
Decrease of current tax expense due to tax holidays ₨ 11,963 ₨ 15,390 ₨ 11,635  
Tax incentives per share | ₨ / shares ₨ 2.05 ₨ 2.56 ₨ 1.84  
Deferred tax liabilities on cumulative earnings of subsidiaries ₨ 56,391 ₨ 52,488    
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 ₨ 2,044 ₨ 3,149