Long-Term Debt - Maturities of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Long-term debt maturing within one year
2025	$ 1,729.0
2026	1,519.4
2027	2,137.3
2028	2,303.2
2029	2,643.4
Thereafter	8,691.6
Total	$ 19,023.9	$ 16,724.3
MGU \| 2.69% MGU Senior Notes due May 2025
Long-term debt maturing within one year
Interest rate	2.69%
Principal amount of unsecured debt	$ 60.0
MERC \| 2.69% MERC Senior Notes due May 2025
Long-term debt maturing within one year
Interest rate	2.69%
Principal amount of unsecured debt	$ 50.0
WE \| 3.10% WE Debentures due June 2025
Long-term debt maturing within one year
Interest rate	3.10%
Principal amount of unsecured debt	$ 250.0
WG \| 3.53% WG Debentures due September 2025
Long-term debt maturing within one year
Interest rate	3.53%
Principal amount of unsecured debt	$ 200.0
WPS \| 5.35% WPS Senior Notes due November 2025
Long-term debt maturing within one year
Interest rate	5.35%
Principal amount of unsecured debt	$ 300.0
ATC Holding LLC \| 4.18% ATC Senior Notes due December 2025
Long-term debt maturing within one year
Interest rate	4.18%
Principal amount of unsecured debt	$ 85.0
WEPCo Environmental Trust Finance I, LLC \| WEPCo Environmental Trust Bonds 1.578%, due 2035
Long-term debt maturing within one year
Interest rate	1.58%
Principal amount of secured debt	$ 9.2
Bluewater Gas Storage \| 3.76% Bluewater Gas Storage senior notes
Long-term debt maturing within one year
Interest rate	3.76%
Principal amount of senior notes	$ 3.0
Bluewater Gas Storage \| 5.41% Bluewater Senior Notes due 11/01/2041
Long-term debt maturing within one year
Interest rate	5.41%
Principal amount of senior notes	$ 0.9
We Power \| 4.91% We Power subsidiaries notes - PWGS
Long-term debt maturing within one year
Interest rate	4.91%
Principal amount of secured debt	$ 8.4
We Power \| 5.209% We Power subsidiaries notes - ERGS
Long-term debt maturing within one year
Interest rate	5.209%
Principal amount of secured debt	$ 16.3
We Power \| 4.673% We Power subsidiaries notes - ERGS
Long-term debt maturing within one year
Interest rate	4.673%
Principal amount of secured debt	$ 12.2
We Power \| 6.00% We Power subsidiaries notes - PWGS
Long-term debt maturing within one year
Interest rate	6.00%
Principal amount of secured debt	$ 7.5
WECI Wind Holding I \| 2.75% WECI Wind Holding I senior notes due 2032
Long-term debt maturing within one year
Interest rate	2.75%
Principal amount of senior notes	$ 44.4
WECI Wind Holding II \| 6.38% WECI Wind Holding II LLC Senior Notes Due 2031
Long-term debt maturing within one year
Interest rate	6.38%
Principal amount of senior notes	$ 19.6
WECI Energy Holding III \| 5.73% WECI Energy Holding III LLC Senior Notes Due 12/31/2039
Long-term debt maturing within one year
Interest rate	5.73%
Principal amount of senior notes	$ 42.5
WEC Energy Group
Long-term debt maturing within one year
2025	620.0
2026	1,350.0
2027	1,762.5
2028	950.0
2029	862.5
Thereafter	$ 1,250.0
WEC Energy Group \| 3.55% WEC Senior Notes due June 2025
Long-term debt maturing within one year
Interest rate	3.55%
Principal amount of unsecured debt	$ 120.0
WEC Energy Group \| 5.00% WEC Senior Notes due September 2025
Long-term debt maturing within one year
Interest rate	5.00%
Principal amount of unsecured debt	$ 500.0

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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