Fair value measurement - Derivative Instruments Measured at Fair Value on Recurring Basis (Detail) ₨ in Millions, $ in Millions	Mar. 31, 2025 INR (₨)	Mar. 31, 2025 USD ($)	Mar. 31, 2024 INR (₨)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	₨ 179,812.4	$ 2,104.8	₨ 109,038.5
Derivative liabilities	143,566.1	$ 1,680.5	109,409.9
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	179,812.4		109,038.5
Derivative liabilities	143,566.1		109,409.9
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Quoted Prices In Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.0		0.0
Derivative liabilities	0.0		0.0
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	179,812.4		109,038.5
Derivative liabilities	143,566.1		109,409.9
Fair Value, Measurements, Recurring \| Fair Value Measurements Using Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.0		0.0
Derivative liabilities	₨ 0.0		₨ 0.0