v3.25.2
Deferred tax assets (DTA) (net) / deferred tax liabilities (DTL) (net) - Summary of Reconciliation of DTA (Net) and DTL (Net) (Detail)
₨ in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2025
INR (₨)
Mar. 31, 2025
USD ($)
Mar. 31, 2024
INR (₨)
Mar. 31, 2023
INR (₨)
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Income / (expense) recognised in profit or loss ₨ (3,929) $ (46) ₨ (3,014) ₨ (1,593)
Income / (expense) recognised in OCI 91   (82) 564
Compound financial instruments        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 2,895   2,554 (12)
Income / (expense) recognised in profit or loss 407   380 85
Income / (expense) recognised in equity (40)   (40) 2,631
Income / (expense) recognised in Adjustment on account of sale of subsidiary     1 (150)
Closing balance 3,262   2,895 2,554
Gain / (loss) on mark to market of derivative instruments        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance (772)   (432) 463
Income / (expense) recognised in profit or loss 28   (268) 0
Income / (expense) recognised in OCI (32)   (84) (895)
Income / (expense) recognised in equity (480)   (275)  
Income / (expense) recognised in Adjustment on account of sale of subsidiary     287  
Closing balance (1,256)   (772) (432)
Difference in written down value as per books of account and tax laws        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance (78,085)   (72,547) (62,551)
Income / (expense) recognised in profit or loss (13,428)   (8,775) (9,996)
Income / (expense) recognised in Adjustment on account of sale of subsidiary 2,463   3,237  
Closing balance (89,050)   (78,085) (72,547)
Unamortised ancillary borrowing cost        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance (319)   (310) (223)
Income / (expense) recognised in profit or loss 63   (10) (87)
Income / (expense) recognised in Adjustment on account of sale of subsidiary     1  
Closing balance (256)   (319) (310)
Provision for decommissioning costs        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 2,525   4,312 3,434
Income / (expense) recognised in profit or loss (234)   (1,750) 878
Income / (expense) recognised in Adjustment on account of sale of subsidiary (15)   (37)  
Closing balance 2,276   2,525 4,312
Expected credit losses        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 422   384 255
Income / (expense) recognised in profit or loss 158   38 129
Closing balance 580   422 384
Fair value gain on financial instruments        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance       (9)
Income / (expense) recognised in profit or loss       9
Unabsorbed depreciation available for offsetting against future taxable income        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 53,947   51,202 43,949
Income / (expense) recognised in profit or loss 8,483   5,160 7,253
Income / (expense) recognised in OCI 42   711  
Income / (expense) recognised in Adjustment on account of sale of subsidiary (2,256)   (3,126)  
Closing balance 60,216   53,947 51,202
Tax Losses available for offsetting against future taxable income        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 2,050   686 425
Income / (expense) recognised in profit or loss 1,111   1,364 (346)
Income / (expense) recognised in OCI       607
Closing balance 3,161   2,050 686
Minimum alternate tax        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 3,034   2,376 1,892
Income / (expense) recognised in profit or loss (20)   658 484
Closing balance 3,014   3,034 2,376
Lease liabilities        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 1,167   724 654
Income / (expense) recognised in profit or loss 287   534 70
Income / (expense) recognised in Adjustment on account of sale of subsidiary (52)   (91)  
Closing balance 1,402   1,167 724
Government grant (viability gap funding)        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 452   405 412
Income / (expense) recognised in profit or loss (98)   47 (7)
Closing balance 354   452 405
Right of use asset        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance (1,174)   (844) (672)
Income / (expense) recognised in profit or loss (148)   (417) (172)
Income / (expense) recognised in Adjustment on account of sale of subsidiary 50   87  
Closing balance (1,272)   (1,174) (844)
Others        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance 709   681 577
Income / (expense) recognised in profit or loss (535)   25 107
Income / (expense) recognised in OCI (10)   3 (3)
Closing balance 161   709 681
Deferred Tax Assets Or Deferred Tax Liabilities        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Opening balance (13,149)   (10,809) (11,406)
Income / (expense) recognised in profit or loss (3,929)   (3,014) (1,593)
Income / (expense) recognised in OCI 0   630 (291)
Income / (expense) recognised in equity (520)   (315) 2,631
Income / (expense) recognised in Adjustment on account of sale of subsidiary 190   359 (150)
Closing balance ₨ (17,408)   ₨ (13,149) ₨ (10,809)