v3.26.1
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, 2026
INR (₨)
Mar. 31, 2026
USD ($)
Mar. 31, 2025
INR (₨)
Mar. 31, 2025
USD ($)
Mar. 31, 2024
INR (₨)
Mar. 31, 2024
USD ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Income / (expense) recognised in profit or loss ₨ 540 $ 6 ₨ (3,929)   ₨ (3,014)  
Income / (expense) recognised in OCI | ₨ ₨ 283   ₨ 91   ₨ (82)  
Compound financial instruments            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   3,262   $ 2,895   $ 2,554
Income / (expense) recognised in profit or loss   (145)   407   380
Income / (expense) recognised in equity       (40)   (40)
Income / (expense) recognised in Adjustment on account of sale of subsidiary   (21)       1
Closing balance   3,096   3,262   2,895
Gain / (loss) on mark to market of derivative instruments            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   (1,256)   (772)   (432)
Income / (expense) recognised in profit or loss   298   28   (268)
Income / (expense) recognised in OCI   (697)   (32)   (84)
Income / (expense) recognised in equity       (480)   (275)
Income / (expense) recognised in Adjustment on account of sale of subsidiary   20       287
Closing balance   (1,635)   (1,256)   (772)
Difference in written down value of PPE and intangibles as per books of account and tax laws            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   (89,050)   (78,085)   (72,547)
Income / (expense) recognised in profit or loss   (20,104)   (13,428)   (8,775)
Addition through business combination   (144)        
Income / (expense) recognised in Adjustment on account of sale of subsidiary   4,303   2,463   3,237
Closing balance   (104,995)   (89,050)   (78,085)
Unamortised ancillary borrowing cost            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   (256)   (319)   (310)
Income / (expense) recognised in profit or loss   31   63   (10)
Income / (expense) recognised in Adjustment on account of sale of subsidiary   (6)       1
Closing balance   (231)   (256)   (319)
Provision for decommissioning costs            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   2,276   2,525   4,312
Income / (expense) recognised in profit or loss   187   (234)   (1,750)
Income / (expense) recognised in Adjustment on account of sale of subsidiary   (17)   (15)   (37)
Closing balance   2,446   2,276   2,525
Expected credit losses            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   580   422   384
Income / (expense) recognised in profit or loss   (208)   158   38
Closing balance   372   580   422
Unabsorbed depreciation available for offsetting against future taxable income            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   60,216   53,947   51,202
Income / (expense) recognised in profit or loss   19,446   8,483   5,160
Income / (expense) recognised in OCI   216   42   711
Income / (expense) recognised in Adjustment on account of sale of subsidiary   (3,584)   (2,256)   (3,126)
Closing balance   76,294   60,216   53,947
Tax Losses available for offsetting against future taxable income            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   3,161   2,050   686
Income / (expense) recognised in profit or loss   (230)   1,111   1,364
Closing balance   2,931   3,161   2,050
Minimum alternate tax            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   3,014   3,034   2,376
Income / (expense) recognised in profit or loss   728   (20)   658
Closing balance   3,742   3,014   3,034
Lease liabilities            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   1,402   1,167   724
Income / (expense) recognised in profit or loss   548   287   534
Income / (expense) recognised in Adjustment on account of sale of subsidiary   (109)   (52)   (91)
Closing balance   1,841   1,402   1,167
Government grant (viability gap funding)            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   354   452   405
Income / (expense) recognised in profit or loss   (20)   (98)   47
Closing balance   334   354   452
Right of use asset            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   (1,272)   (1,174)   (844)
Income / (expense) recognised in profit or loss   (400)   (148)   (417)
Income / (expense) recognised in Adjustment on account of sale of subsidiary   93   50   87
Closing balance   (1,579)   (1,272)   (1,174)
Others            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   161   709   681
Income / (expense) recognised in profit or loss   409   (538)   25
Income / (expense) recognised in OCI   6   (10)   3
Closing balance   576   161   709
Deferred Tax Assets Or Deferred Tax Liabilities            
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]            
Opening balance   (17,408)   (13,149)   (10,809)
Income / (expense) recognised in profit or loss   540   (3,929)   (3,014)
Income / (expense) recognised in OCI   (475)   0   630
Income / (expense) recognised in equity       (520)   (315)
Addition through business combination   (144)        
Income / (expense) recognised in Adjustment on account of sale of subsidiary   679   190   359
Closing balance   $ (16,808)   $ (17,408)   $ (13,149)