LONG-TERM DEBT (Details)	1 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2025 USD ($) d $ / shares	May 31, 2025 USD ($)	Apr. 30, 2025 USD ($)	Jun. 30, 2025 USD ($) $ / shares	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) $ / shares	Jun. 30, 2024 USD ($)
Debt Instrument [Line Items]
Interest expense				$ 220,800,000	$ 200,600,000	$ 443,800,000	$ 392,600,000
3.10% WE Debentures due June 1, 2025 | WE
Debt Instrument [Line Items]
Repayment of long-term debt	$ 250,000,000.0
Interest rate on long-term debt	3.10%			3.10%		3.10%
5.20% MERC Senior Notes due 5/1/2030 | MERC
Debt Instrument [Line Items]
Interest rate on long-term debt			5.20%
Proceeds from issuance of debt			$ 50,000,000.0
2.69% MERC Senior Notes due 5/1/2025 | MERC
Debt Instrument [Line Items]
Repayment of long-term debt		$ 50,000,000
Interest rate on long-term debt		2.69%
5.20% MGU Senior Notes due 5/1/2030 | MGU
Debt Instrument [Line Items]
Interest rate on long-term debt			5.20%
Proceeds from issuance of debt			$ 75,000,000.0
2.69% MGU Senior Notes due 5/1/2025 | MGU
Debt Instrument [Line Items]
Repayment of long-term debt		$ 60,000,000
Interest rate on long-term debt		2.69%
WEC Energy Group | WEC 3.55% Senior Notes $120M due June 1, 2025
Debt Instrument [Line Items]
Repayment of long-term debt	$ 120,000,000.0
Interest rate on long-term debt	3.55%			3.55%		3.55%
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028
Debt Instrument [Line Items]
Interest rate on long-term debt	3.375%			3.375%		3.375%
Proceeds from convertible debt	$ 900,000,000.0
Principal amount conversion rate applied to	$ 1,000			$ 1,000		$ 1,000
Initial conversion ratio	7.7901
Initial conversion price, per share | $ / shares	$ 128.37			$ 128.37		$ 128.37
Senior Notes	$ 900,000,000.0			$ 900,000,000.0		$ 900,000,000.0
Unamortized debt issuance costs	(11,200,000)			(11,200,000)		(11,200,000)
Net carrying amount	888,800,000			888,800,000		888,800,000
Fair value amount	$ 902,900,000			902,900,000		902,900,000
Contractual interest expense				1,800,000	0	1,800,000	0
Amortization of debt issuance costs				300,000	0	300,000	0
Interest expense				2,100,000	0	2,100,000	0
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Early redemption terms
Debt Instrument [Line Items]
Debt instrument, redemption price, percentage	100.00%
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms one
Debt Instrument [Line Items]
Trading days | d	20
Consecutive trading days | d	30
Threshold percentage of trigger	130.00%
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms two
Debt Instrument [Line Items]
Trading days | d	5
Consecutive trading days | d	10
Threshold percentage of trigger	98.00%
Principal amount conversion rate applied to	$ 1,000			1,000		1,000
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms three
Debt Instrument [Line Items]
Trading days prior to redemption | d	2
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2027
Debt Instrument [Line Items]
Senior Notes	$ 862,500,000			862,500,000		862,500,000
Unamortized debt issuance costs	(6,400,000)			(6,400,000)		(6,400,000)
Net carrying amount	856,100,000			856,100,000		856,100,000
Fair value amount	968,500,000			968,500,000		968,500,000
Contractual interest expense				9,500,000	3,500,000	18,900,000	3,500,000
Amortization of debt issuance costs				900,000	300,000	1,700,000	300,000
Interest expense				10,400,000	3,800,000	20,600,000	3,800,000
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2029
Debt Instrument [Line Items]
Senior Notes	862,500,000			862,500,000		862,500,000
Unamortized debt issuance costs	(7,800,000)			(7,800,000)		(7,800,000)
Net carrying amount	854,700,000			854,700,000		854,700,000
Fair value amount	$ 991,100,000			991,100,000		991,100,000
Contractual interest expense				9,500,000	3,500,000	18,900,000	3,500,000
Amortization of debt issuance costs				500,000	200,000	1,000,000.0	200,000
Interest expense				$ 10,000,000.0	$ 3,700,000	$ 19,900,000	$ 3,700,000