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Financial Instruments - Summary of Significant Unobservable Inputs to Valuation (Detail) - INR (₨)
₨ in Millions
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Unquoted equity investments [member] | Market multiple approach [member] | Revenue multiple [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique   Market multiple approach
Significant unobservable input   Revenue multiple
Movement by   0.5x
Increase   ₨ 179
Decrease   ₨ (186)
Unquoted equity investments [member] | Third party quote [member] | Forecast Revenues [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique Third party quote  
Significant unobservable input Forecast revenues  
Movement by 1.00%  
Increase ₨ 18  
Decrease ₨ (18)  
Unquoted equity investments [member] | Discounted cash flow model [member] | Long term growth rate [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique   Discounted cash flow model
Significant unobservable input   Long-term growth rate
Movement by   0.50%
Increase   ₨ 55
Decrease   ₨ (51)
Unquoted equity investments [member] | Discounted cash flow model [member] | Discount rate [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Significant unobservable input   Discount rate
Movement by   0.50%
Increase   ₨ (93)
Decrease   ₨ 101
Derivative assets [member] | Market multiple approach [member] | Time to liquidation event [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Significant unobservable input   Time to liquidation event
Movement by   1 year
Increase   ₨ 60
Decrease   ₨ (69)
Derivative assets [member] | Option pricing model [member] | Volatility of comparable companies [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique   Option pricing model
Significant unobservable input   Volatility of comparable companies
Movement by   2.50%
Increase   ₨ 31
Decrease   ₨ (31)
Contingent consideration [member] | Probability weighted method [member] | Estimated revenue achievement [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique   Probability weighted method
Significant unobservable input   Estimated revenue achievement
Movement by   5.00%
Increase   ₨ 56
Decrease   ₨ (56)
Contingent consideration [member] | Probability weighted method [member] | Estimated earnings achievement [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Significant unobservable input   Estimated earnings achievement
Movement by   1.00%