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Employee Benefits (Tables)
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Reconciliation of the changes in the plans' benefit obligations and fair value of assets
The following tables provide a reconciliation of the changes in our plans' benefit obligations and fair value of assets:
Pension BenefitsOPEB Benefits
(in millions)2024202320242023
Change in benefit obligation
Obligation at January 1$2,352.4 $2,315.9 $448.1 $402.3 
Service cost24.2 24.0 10.9 9.8 
Interest cost116.6 122.3 22.7 21.6 
Participant contributions— — 11.2 11.8 
Actuarial (gain) loss(99.6)81.9 6.9 45.9 
Benefit payments(184.4)(191.7)(41.7)(46.0)
Federal subsidy on benefits paidN/AN/A1.4 1.5 
Transfer— — 1.4 1.2 
Obligation at December 31$2,209.2 $2,352.4 $460.9 $448.1 
Change in fair value of plan assets
Fair value at January 1$2,665.8 $2,628.0 $829.6 $835.3 
Actual return on plan assets129.8 214.9 49.5 76.4 
Employer contributions net of plan transfer (1)
13.1 14.6 1.4 (47.9)
Participant contributions— — 11.2 11.8 
Benefit payments(184.4)(191.7)(41.7)(46.0)
Fair value at December 31$2,624.3 $2,665.8 $850.0 $829.6 
Funded status at December 31$415.1 $313.4 $389.1 $381.5 

(1)    Employer contribution includes a $50.0 million transfer out of the WEC Energy Group Retiree Welfare Plan, in 2023, associated with the overfunded position of this plan.
Amounts recognized on the balance sheets at December 31 related to the funded status of the benefit plans
The amounts recognized on our balance sheets at December 31 related to the funded status of the benefit plans were as follows:
Pension BenefitsOPEB Benefits
(in millions)2024202320242023
Pension and OPEB assets$562.4 $475.2 $406.1 $395.7 
Other long-term liabilities147.3 161.8 17.0 14.2 
Total net assets$415.1 $313.4 $389.1 $381.5 
Defined Benefit Plan Disclosure [Line Items]  
Amounts that had not yet been recognized in the entity's net periodic benefit cost
The following table shows the amounts that had not yet been recognized in our net periodic benefit cost (credit) as of December 31:
Pension BenefitsOPEB Benefits
(in millions)2024202320242023
Pre-tax accumulated other comprehensive income (loss) (1)
Net actuarial loss (gain)$12.3 $12.7 $(1.1)$(1.2)
Prior service credits— — — — 
Total$12.3 $12.7 $(1.1)$(1.2)
Net regulatory assets (liabilities) (2)
Net actuarial loss (gain)$578.7 $688.9 $(148.8)$(166.3)
Prior service credits(2.1)(2.2)(15.8)(29.3)
Total$576.6 $686.7 $(164.6)$(195.6)

(1)    Amounts related to the nonregulated entities are included in accumulated other comprehensive loss.

(2)    Amounts related to the utilities and WBS are recorded as net regulatory assets or liabilities.
Schedule of the components of net periodic benefit cost
The components of net periodic benefit cost (credit) (including amounts capitalized to our balance sheets) for the years ended December 31 were as follows:
Pension BenefitsOPEB Benefits
(in millions)202420232022202420232022
Service cost$24.2 $24.0 $50.8 $10.9 $9.8 $14.3 
Interest cost116.6 122.3 91.8 22.7 21.6 15.4 
Expected return on plan assets(182.1)(187.4)(208.0)(52.7)(53.0)(68.9)
Plan settlement4.0 1.3 6.2 — — — 
Amortization of prior service cost (credit)(0.1)— 1.6 (13.5)(14.8)(15.9)
Amortization of net actuarial loss (gain)59.5 33.0 75.3 (7.6)(12.3)(24.7)
Net periodic benefit cost (credit)$22.1 $(6.8)$17.7 $(40.2)$(48.7)$(79.8)
Weighted-average assumptions used to determine benefit obligations and net periodic benefit cost for the plans
The weighted-average assumptions used to determine the benefit obligations for the plans were as follows for the years ended December 31:
Pension BenefitsOPEB Benefits
2024202320242023
Discount rate5.69%5.19%5.71%5.16%
Rate of compensation increase4.00%4.00%N/AN/A
Interest credit rate4.85%4.84%N/AN/A
Assumed medical cost trend rate (Pre 65)N/AN/A7.00%6.25%
Ultimate trend rate (Pre 65)N/AN/A5.00%5.00%
Year ultimate trend rate is reached (Pre 65)N/AN/A20332031
Assumed medical cost trend rate (Post 65)N/AN/A6.10%6.39%
Ultimate trend rate (Post 65)N/AN/A5.00%5.00%
Year ultimate trend rate is reached (Post 65)N/AN/A20302030

The weighted-average assumptions used to determine the net periodic benefit cost for the plans were as follows for the years ended December 31:
Pension Benefits
202420232022
Discount rate5.18%5.49%3.18%
Expected return on plan assets6.61%6.62%6.88%
Rate of compensation increase4.00%4.00%4.00%
Interest credit rate4.84%4.62%3.78%

OPEB Benefits
202420232022
Discount rate5.16%5.50%2.92%
Expected return on plan assets6.50%6.50%7.00%
Assumed medical cost trend rate (Pre 65)6.25%6.50%5.70%
Ultimate trend rate (Pre 65)5.00%5.00%5.00%
Year ultimate trend rate is reached (Pre 65)203120312028
Assumed medical cost trend rate (Post 65)6.39%6.00%5.67%
Ultimate trend rate (Post 65)5.00%5.00%5.00%
Year ultimate trend rate is reached (Post 65)203020312028
Investments recorded at fair value, by asset class
The following tables provide the fair values of our investments by asset class:
December 31, 2024
Pension Plan AssetsOPEB Assets
(in millions)Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Asset Class
Equity securities:
United States equity$168.4 $— $— $168.4 $93.8 $— $— $93.8 
International equity158.2 — — 158.2 86.4 — — 86.4 
Fixed income securities: (1)
United States bonds— 880.1 — 880.1 99.0 205.6 — 304.6 
International bonds— 81.6 — 81.6 — 11.2 — 11.2 
$326.6 $961.7 $— $1,288.3 $279.2 $216.8 $— $496.0 
Investments measured at net asset value:
Equity securities414.9 190.4 
Fixed income securities126.0 51.8 
Other795.1 111.8 
Total$2,624.3 $850.0 

(1)    This category represents investment grade bonds of United States and foreign issuers denominated in United States dollars from diverse industries.
December 31, 2023
Pension Plan AssetsOPEB Assets
(in millions)Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Asset Class
Equity securities:
United States equity$179.3 $— $— $179.3 $91.8 $— $— $91.8 
International equity174.0 — — 174.0 84.6 — — 84.6 
Fixed income securities: (1)
United States bonds— 906.6 — 906.6 91.5 203.2 — 294.7 
International bonds— 88.0 — 88.0 — 11.9 — 11.9 
$353.3 $994.6 $— $1,347.9 $267.9 $215.1 $— $483.0 
Investments measured at net asset value:
Equity securities407.4 182.1 
Fixed income securities124.2 47.7 
Other786.3 116.8 
Total$2,665.8 $829.6 

(1)    This category represents investment grade bonds of United States and foreign issuers denominated in United States dollars from diverse industries.
Schedule of expected future benefit payments
The following table shows the payments, reflecting expected future service, that we expect to make for pension and OPEB over the next 10 years:
(in millions)Pension BenefitsOPEB Benefits
2025$212.5 $35.3 
2026214.4 36.7 
2027205.0 37.9 
2028197.2 38.5 
2029188.7 38.8 
2030-2034839.4 189.4 
Pension Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
The following table shows information for pension plans with an accumulated benefit obligation in excess of plan assets. Amounts presented are as of December 31:
(in millions)20242023
Accumulated benefit obligation$286.0 $300.7 
Fair value of plan assets143.2 147.3 
Information for pension plans with a projected benefit obligation in excess of plan assets
The following table shows information for pension plans with a projected benefit obligation in excess of plan assets. Amounts presented are as of December 31:
(in millions)20242023
Projected benefit obligation$290.5 $306.7 
Fair value of plan assets143.2 147.3 
OPEB Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
The following table shows information for OPEB plans with an accumulated benefit obligation in excess of plan assets. Amounts presented are as of December 31:
(in millions)20242023
Accumulated benefit obligation$194.0 $21.0 
Fair value of plan assets177.0 6.9