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Financial Instruments - Summary of Significant Unobservable Inputs to Valuation (Parenthetical) (Detail) - INR (₨)
₨ in Millions
Mar. 31, 2018
Mar. 31, 2017
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [Abstract]    
Unquoted equity investments ₨ 1,545 ₨ 3,232