FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments			$ 2,407.0	$ 2,398.0
I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments			2,386.5	2,389.0
Spent Nuclear Fuel and Decommissioning Trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	$ 1,037.8	$ 1,181.9	2,332.2	2,336.0
Purchases of Investments	1,056.5	1,201.9	2,386.5	2,389.0
Gross Realized Gains on Investment Sales	112.5	108.4	116.8	118.7
Gross Realized Losses on Investment Sales	1.5	0.7	4.0	6.1
Spent Nuclear Fuel and Decommissioning Trusts \| I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	1,037.8	1,181.9	2,332.2	2,336.0
Purchases of Investments	1,056.5	1,201.9	2,386.5	2,389.0
Gross Realized Gains on Investment Sales	112.5	108.4	116.8	118.7
Gross Realized Losses on Investment Sales	$ 1.5	$ 0.7	$ 4.0	$ 6.1

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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