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v3.25.1

LONG-TERM DEBT (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended
--- | --- | ---
May 31, 2025 | Apr. 30, 2025 | Mar. 31, 2025 | Mar. 31, 2024
Debt Instrument [Line Items] |  |  |  |
Interest expense |  |  | $ 223.0 | $ 192.0
5.20% MERC Senior Notes due 5/1/2030 | MERC | Subsequent event |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of debt |  | $ 50.0 |  |
Interest rate on long-term debt |  | 5.20% |  |
5.20% MGU Senior Notes due 5/1/2030 | MGU | Subsequent event |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of debt |  | $ 75.0 |  |
Interest rate on long-term debt |  | 5.20% |  |
2.69% MGU Senior Notes due 5/1/2025 | MGU | Subsequent event |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate on long-term debt | 2.69% |  |  |
Repayment of long-term debt | $ 60.0 |  |  |
2.69% MERC Senior Notes due 5/1/2025 | MERC | Subsequent event |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate on long-term debt | 2.69% |  |  |
Repayment of long-term debt | $ 50.0 |  |  |
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2027 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior Notes |  |  | 862.5 |
Unamortized debt issuance costs |  |  | (7.2) |
Net carrying amount |  |  | 855.3 |
Fair value amount |  |  | 1,009.0 |
Contractual interest expense |  |  | 9.4 |
Amortization of debt issuance costs |  |  | 0.8 |
Interest expense |  |  | 10.2 |
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2029 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior Notes |  |  | 862.5 |
Unamortized debt issuance costs |  |  | (8.3) |
Net carrying amount |  |  | 854.2 |
Fair value amount |  |  | 1,029.2 |
Contractual interest expense |  |  | 9.4 |
Amortization of debt issuance costs |  |  | 0.5 |
Interest expense |  |  | $ 9.9 |

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