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Loans and Borrowings - Additional Information (Detail)
€ in Millions, ₨ in Millions, ر.س in Millions, £ in Millions, Rp in Millions, $ in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2018
INR (₨)
Mar. 31, 2017
INR (₨)
Mar. 31, 2018
EUR (€)
Mar. 31, 2018
USD ($)
Mar. 31, 2018
GBP (£)
Mar. 31, 2018
SAR (ر.س)
Mar. 31, 2018
CAD ($)
Mar. 31, 2018
IDR (Rp)
Disclosure of detailed information about borrowings [line items]                
Obligations under finance leases ₨ 5,442 ₨ 8,280            
Interest expense ₨ 3,045 1,916            
Bottom of range [member]                
Disclosure of detailed information about borrowings [line items]                
Finance lease contract term 1 year              
Top of range [member]                
Disclosure of detailed information about borrowings [line items]                
Finance lease contract term 5 years              
Bank overdraft [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings ₨ 79,598 116,742            
Line of credit [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings 10,000              
Line of credit [member] | U.S.Dollar [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | $       $ 1,748        
Remaining borrowing capacity | $       $ 711        
Line of credit [member] | Canadian Dollar [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | $             $ 57  
Remaining borrowing capacity | $             $ 27  
Line of credit [member] | EURO [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | €     € 19          
Remaining borrowing capacity | €     € 2          
Line of credit [member] | Great British Pound [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | £         £ 43      
Remaining borrowing capacity | £         £ 42      
Line of credit [member] | Indonesia, Rupiahs                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | Rp               Rp 13,000
Remaining borrowing capacity | Rp               Rp 13,000
Line of credit [member] | Saudi Arabian Riyal [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings | ر.س           ر.س 43    
Remaining borrowing capacity | ر.س           ر.س 39    
Line of credit [member] | Indian Rupee [member]                
Disclosure of detailed information about borrowings [line items]                
Remaining borrowing capacity 1,003              
Revolving credit facilities non-fund based [member]                
Disclosure of detailed information about borrowings [line items]                
Short-term borrowings 44,022 51,739            
Remaining borrowing capacity ₨ 22,476 ₨ 29,716