v3.25.2
FAIR VALUE MEASUREMENTS - Summary of Nuclear Trust Investments (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2025
Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value $ 4,609.7 $ 4,395.1
Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 2,468.7 2,297.8
Gross Unrealized Losses (10.5) (15.5)
Other-Than-Temporary Impairments (24.0) (26.0)
I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 4,609.7 4,395.1
I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 2,468.7 2,297.8
Gross Unrealized Losses (10.5) (15.5)
Other-Than-Temporary Impairments (24.0) (26.0)
Cash and Cash Equivalents    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 28.1 23.3
Cash and Cash Equivalents | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Other-Than-Temporary Impairments 0.0 0.0
Cash and Cash Equivalents | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 28.1 23.3
Cash and Cash Equivalents | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Other-Than-Temporary Impairments 0.0 0.0
United States Government    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 1,298.6 1,322.8
United States Government | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 3.3 8.2
Gross Unrealized Losses (9.0) (5.3)
Other-Than-Temporary Impairments (16.9) (20.2)
United States Government | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 1,298.6 1,322.8
United States Government | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 3.3 8.2
Gross Unrealized Losses (9.0) (5.3)
Other-Than-Temporary Impairments (16.9) (20.2)
Corporate Debt    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 274.8 211.3
Corporate Debt | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 20.5 0.7
Gross Unrealized Losses (1.0) (9.8)
Other-Than-Temporary Impairments (7.1) (5.8)
Corporate Debt | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 274.8 211.3
Corporate Debt | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 20.5 0.7
Gross Unrealized Losses (1.0) (9.8)
Other-Than-Temporary Impairments (7.1) (5.8)
State and Local Government    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 0.0 0.0
State and Local Government | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Other-Than-Temporary Impairments 0.0 0.0
State and Local Government | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 0.0 0.0
State and Local Government | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Other-Than-Temporary Impairments 0.0 0.0
Subtotal Fixed Income Securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 1,573.4 1,534.1
Subtotal Fixed Income Securities | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 23.8 8.9
Gross Unrealized Losses (10.0) (15.1)
Other-Than-Temporary Impairments (24.0) (26.0)
Subtotal Fixed Income Securities | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 1,573.4 1,534.1
Subtotal Fixed Income Securities | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 23.8 8.9
Gross Unrealized Losses (10.0) (15.1)
Other-Than-Temporary Impairments (24.0) (26.0)
Equity Securities - Domestic    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 3,008.2 2,837.7
Equity Securities - Domestic | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 2,444.9 2,288.9
Gross Unrealized Losses (0.5) (0.4)
Other-Than-Temporary Impairments 0.0 0.0
Equity Securities - Domestic | I&M    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value 3,008.2 2,837.7
Equity Securities - Domestic | I&M | Spent Nuclear Fuel and Decommissioning Trusts    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Gross Unrealized Gains 2,444.9 2,288.9
Gross Unrealized Losses (0.5) (0.4)
Other-Than-Temporary Impairments $ 0.0 $ 0.0