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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
	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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