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DISCONTINUED OPERATIONS - Narrative (Details) ₨ / shares in Units, shares in Millions, ₨ in Billions |  |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |
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Sep. 12, 2024 USD ($) | Jun. 05, 2024 USD ($) | Jun. 05, 2024 INR (₨) | Apr. 29, 2024 USD ($) shares | Apr. 29, 2024 INR (₨) ₨ / shares shares | Mar. 23, 2024 USD ($) shares | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2024 INR (₨) | Sep. 12, 2024 INR (₨) | Jun. 05, 2024 INR (₨) | Mar. 23, 2024 INR (₨) | Jan. 04, 2024 USD ($) | Jan. 04, 2024 INR (₨) | Feb. 28, 2023 USD ($) | Feb. 28, 2023 INR (₨)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss on sale of ATC TIPL |  |  |  |  |  |  |  |  | $ 0 | $ 1,245,500,000 |  |  |  |  |  |  |  |  |
VIL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of converted shares | shares |  |  |  |  |  | 1,440 |  |  |  |  |  |  |  |  |  |  |  |  |
Equity shares sold (in shares) | shares |  |  |  | 1,440 | 1,440 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price per share (in INR per share) | ₨ / shares |  |  |  |  | ₨ 12.78 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  | $ 216,000,000 | ₨ 18.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity securities |  |  |  |  |  |  |  | $ 0 |  | 0 |  |  |  |  |  |  |  |  |
OCDs | VIL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt securities |  | $ 19,200,000 |  |  |  | $ 172,700,000 |  | 0 |  | 0 |  |  |  | ₨ 1.6 | ₨ 14.4 |  |  |  |
Not proceeds from sale of debt securities |  | $ 22,000,000 | ₨ 1.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
OCDs | VIL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
VIL OCDs, face value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 193,200,000 | ₨ 16.0
Debt securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 116,500,000 |
Debt securities, interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11.20% | 11.20%
OCDs | VIL | Maturing on August 27, 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
VIL OCDs, face value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 96,600,000 | ₨ 8.0
OCDs | VIL | Maturing on August 27, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
VIL OCDs, face value | ₨ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | ₨ 8.0
ATC TIPL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution received |  |  |  |  |  |  |  |  |  |  | $ 354,100,000 | ₨ 29.6 |  |  |  |  |  |  |
Discontinued Operations, Disposed of by Sale | ATC TIPL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interest sold | 100.00% |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |
Maximum consideration to be received upon disposal |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,500,000,000 | ₨ 210.0 |  |
Total consideration received upon disposal | $ 2,200,000,000 |  |  |  |  |  |  | 2,158,800,000 |  | 2,158,800,000 |  |  | ₨ 182.0 |  |  |  |  |  |
Loss on sale of ATC TIPL |  |  |  |  |  |  | $ 0 | 1,245,500,000 | $ 0 | 1,245,500,000 |  |  |  |  |  |  |  |  |
Reclassification of cumulative translation adjustment | $ 1,100,000,000 |  |  |  |  |  |  | $ 1,100,000,000 |  | 1,072,300,000 |  |  |  |  |  |  |  |  |
Discontinued Operations, Disposed of by Sale | ATC TIPL | VIL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on sales of investments included in discontinued operations |  |  |  |  |  |  |  |  |  | $ 46,400,000 |  |  |  |  |  |  |  |  |

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