GOODWILL AND INTANGIBLES - FINITE-LIVED INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2025	Dec. 31, 2024
Finite-Lived Intangible Assets
Period of amortization	5 years
Amortization to be recorded as a decrease to operating revenues
Amortization to be recorded in the next five years
2025	$ 57.9
2026	59.9
2027	59.9
2028	59.9
2029	59.9
Maple Flats \| Amortization to be recorded as a decrease to operating revenues
Amortization to be recorded in the next five years
2025	1.3
2026	1.3
2027	1.3
2028	1.3
2029	1.3
PPAs \| Maple Flats
Finite-Lived Intangible Assets
Gross carrying amount	$ 18.8	$ 13.0
Weighted average remaining useful life	15 years
Period of amortization	5 years

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-2

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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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.

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 350
-SubTopic 30
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-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
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-Section 50
-Paragraph 2
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Period of amortization over a future period of time

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