Employee Benefits - Change in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Change in benefit obligation
Obligation at January 1	$ 2,352.4	$ 2,315.9
Service cost	24.2	24.0	$ 50.8
Interest cost	116.6	122.3	91.8
Participant contributions	0.0	0.0
Actuarial (gain) loss	(99.6)	81.9
Benefit payments	(184.4)	(191.7)
Transfer	0.0	0.0
Obligation at December 31	2,209.2	2,352.4	2,315.9
Change in fair value of plan assets
Beginning balance at January 1	2,665.8	2,628.0
Actual return on plan assets	129.8	214.9
Employer contributions net of plan transfer	13.1	14.6
Participant contributions	0.0	0.0
Benefit payments	(184.4)	(191.7)
Ending balance at December 31	2,624.3	2,665.8	2,628.0
Funded status at December 31	415.1	313.4
OPEB Benefits
Change in benefit obligation
Obligation at January 1	448.1	402.3
Service cost	10.9	9.8	14.3
Interest cost	22.7	21.6	15.4
Participant contributions	11.2	11.8
Actuarial (gain) loss	6.9	45.9
Benefit payments	(41.7)	(46.0)
Federal subsidy on benefits paid	1.4	1.5
Transfer	1.4	1.2
Obligation at December 31	460.9	448.1	402.3
Change in fair value of plan assets
Beginning balance at January 1	829.6	835.3
Actual return on plan assets	49.5	76.4
Employer contributions net of plan transfer	1.4	(47.9)
Participant contributions	11.2	11.8
Benefit payments	(41.7)	(46.0)
Ending balance at December 31	850.0	829.6	$ 835.3
Funded status at December 31	$ 389.1	381.5
Amount transferred out of WEC Energy Group Retiree Welfare Plan		$ 50.0