Employee benefits (Details 7) - INR (₨) ₨ in Millions	12 Months Ended
Employee benefits (Details 7) - INR (₨) ₨ in Millions	Mar. 31, 2026	Mar. 31, 2025
Not later than one year [Member]
Expected benefit payments in next few years [Abstract]
Estimate of contributions expected to be paid to plan for next annual reporting period	₨ 104	₨ 80
Later than two year and not later than five year [Member]
Expected benefit payments in next few years [Abstract]
Estimate of contributions expected to be paid to plan for next annual reporting period	330	276
Later than six year and not later than ten year [Member]
Expected benefit payments in next few years [Abstract]
Estimate of contributions expected to be paid to plan for next annual reporting period	200	177
Later than ten years [Member]
Expected benefit payments in next few years [Abstract]
Estimate of contributions expected to be paid to plan for next annual reporting period	₨ 106	₨ 97