Retirement benefits - Reconciliation of All Plan Investment Assets Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Detail) - Plan investment funds managed by insurance companies ₨ in Millions, $ in Millions	12 Months Ended
Mar. 31, 2026 INR (₨)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 INR (₨)
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	₨ 769.1	$ 8.2	₨ 859.1
Realized interest credited to fund	59.9	0.6	70.2
Contribution during the period	191.6	2.0	88.6
Amount paid towards claim	(180.4)	(1.9)	(248.8)
Ending Balance	₨ 840.2	$ 8.9	₨ 769.1

Retirement benefits - Reconciliation of All Plan Investment Assets Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Detail) - Plan investment funds managed by insurance companies
₨ in Millions, $ in Millions

12 Months Ended

Mar. 31, 2026

INR (₨)

Mar. 31, 2026

USD ($)

Mar. 31, 2025

INR (₨)

Defined Benefit Plan Disclosure [Line Items]

Beginning balance

₨ 769.1

$ 8.2

₨ 859.1

Realized interest credited to fund

59.9

0.6

70.2

Contribution during the period

191.6

2.0

88.6

Amount paid towards claim

(180.4)

(1.9)

(248.8)

Ending Balance

₨ 840.2

$ 8.9

₨ 769.1

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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+ Details