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LONG-TERM DEBT - CONVERTIBLE DEBT (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025
Debt Instrument [Line Items] |  |  |  |
Interest expense | $ 228.9 | $ 220.8 | $ 457.4 | $ 443.8
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2027 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior Notes | 862.5 |  | 862.5 |
Unamortized debt issuance costs | (3.0) |  | (3.0) |
Net carrying amount | 859.5 |  | 859.5 |
Fair value amount | 1,044.2 |  | 1,044.2 |
Contractual interest expense | 9.5 | 9.5 | 18.9 | 18.9
Amortization of debt issuance costs | 0.9 | 0.9 | 1.7 | 1.7
Interest expense | 10.4 | 10.4 | 20.6 | 20.6
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior Notes | 900.0 |  | 900.0 |
Unamortized debt issuance costs | (6.8) |  | (6.8) |
Net carrying amount | 893.2 |  | 893.2 |
Fair value amount | 936.0 |  | 936.0 |
Contractual interest expense | 7.6 | 1.8 | 15.2 | 1.8
Amortization of debt issuance costs | 0.9 | 0.3 | 1.8 | 0.3
Interest expense | 8.5 | 2.1 | 17.0 | 2.1
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2029 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior Notes | 862.5 |  | 862.5 |
Unamortized debt issuance costs | (5.8) |  | (5.8) |
Net carrying amount | 856.7 |  | 856.7 |
Fair value amount | 1,069.2 |  | 1,069.2 |
Contractual interest expense | 9.5 | 9.5 | 18.9 | 18.9
Amortization of debt issuance costs | 0.5 | 0.5 | 1.0 | 1.0
Interest expense | $ 10.0 | $ 10.0 | $ 19.9 | $ 19.9

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