v3.26.1
Retirement benefits - Plan Investment Assets for Gratuity Funds and Pension Fund Measured at Fair Value by Level and in Total (Detail)
₨ in Millions, $ in Millions
Mar. 31, 2026
INR (₨)
Mar. 31, 2026
USD ($)
Mar. 31, 2025
INR (₨)
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value ₨ 935.1 $ 10.0 ₨ 649.8
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) | Funds managed by insurance company (1)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) | Funds managed by insurance company (2)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) | Government Securities Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) | Debenture and Bonds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1) | Other Funds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 935.1   649.8
Fair Value Measurements Using Significant other observable inputs (Level 2)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 19,713.0 210.0 18,972.6
Fair Value Measurements Using Significant other observable inputs (Level 2) | Funds managed by insurance company (1)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Significant other observable inputs (Level 2) | Funds managed by insurance company (2)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 16,703.4   15,803.1
Fair Value Measurements Using Significant other observable inputs (Level 2) | Government Securities Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 1,491.7   1,799.5
Fair Value Measurements Using Significant other observable inputs (Level 2) | Debenture and Bonds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 1,456.0   1,131.1
Fair Value Measurements Using Significant other observable inputs (Level 2) | Other Funds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 61.9   238.9
Fair Value Measurements Using Significant unobservable inputs (Level 3)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 840.2 $ 9.0 769.1
Fair Value Measurements Using Significant unobservable inputs (Level 3) | Funds managed by insurance company (1)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 840.2   769.1
Fair Value Measurements Using Significant unobservable inputs (Level 3) | Funds managed by insurance company (2)      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Significant unobservable inputs (Level 3) | Government Securities Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Significant unobservable inputs (Level 3) | Debenture and Bonds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value 0.0   0.0
Fair Value Measurements Using Significant unobservable inputs (Level 3) | Other Funds Managed by Trust      
Defined Benefit Plan Disclosure [Line Items]      
Plan investment assets at fair value ₨ 0.0   ₨ 0.0