Fair value measurement - Derivative Instruments Measured at Fair Value on Recurring Basis (Detail) ₨ in Millions, $ in Millions	Mar. 31, 2026 INR (₨)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 INR (₨)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	₨ 624,206.5	$ 6,652.4	₨ 179,812.4
Derivative liabilities	578,276.3	$ 6,162.9	143,566.1
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	624,206.5		179,812.4
Derivative liabilities	578,276.3		143,566.1
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	624,206.5		179,812.4
Derivative liabilities	578,276.3		143,566.1
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

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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