FAIR VALUE MEASUREMENTS - Fixed Income Securities Held in Nuclear Trusts (Details) - Spent Nuclear Fuel and Decommissioning Trusts $ in Millions	Mar. 31, 2025 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	$ 344.0
After 1 year through 5 years	601.9
After 5 years through 10 years	268.9
After 10 years	353.3
Total	1,568.1
I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	344.0
After 1 year through 5 years	601.9
After 5 years through 10 years	268.9
After 10 years	353.3
Total	$ 1,568.1

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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