FAIR VALUE MEASUREMENTS - Fixed Income Securities Held in Nuclear Trusts (Details) - Spent Nuclear Fuel and Decommissioning Trusts $ in Millions	Jun. 30, 2025 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	$ 350.0
After 1 year through 5 years	635.8
After 5 years through 10 years	231.2
After 10 years	356.4
Total	1,573.4
I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	350.0
After 1 year through 5 years	635.8
After 5 years through 10 years	231.2
After 10 years	356.4
Total	$ 1,573.4

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