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Fair Values of Credit Substitutes by Type of Instrument (Detail) ₨ in Millions, $ in Millions | Mar. 31, 2019 INR (₨) | Mar. 31, 2019 USD ($) | Mar. 31, 2018 INR (₨)
--- | --- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | ₨ 2,617,505.3 | $ 37,847.2 | ₨ 2,228,983.3
Fair Value | 2,633,348.4 | 38,076.2 | 2,221,443.3
Debt securities, other than asset and mortgage-backed securities | Credit Substitutes |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 273,550.7 | 3,955.3 | 325,159.3
Fair Value | 272,886.8 | $ 3,945.8 | 324,031.5
Debt securities, other than asset and mortgage-backed securities | Credit Substitutes | Debentures |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 247,869.1 |  | 290,893.5
Fair Value | 247,152.5 |  | 289,782.9
Debt securities, other than asset and mortgage-backed securities | Credit Substitutes | Commercial paper |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 25,681.6 |  | 34,265.8
Fair Value | ₨ 25,734.3 |  | ₨ 34,248.6

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