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Pension and Other Postretirement Benefit Plans (Tables)
12 Months Ended
Dec. 31, 2023
Retirement Benefits [Abstract]  
Obligation and Funded Status
Pension Obligation and Funded Status
As of December 3120232022
Millions  
Accumulated Benefit Obligation$729.5 $724.5 
Change in Benefit Obligation  
Obligation, Beginning of Year$739.7 $911.7 
Service Cost6.5 9.3 
Interest Cost40.5 27.2 
Plan Amendments— 0.8 
Actuarial (Gain) Loss (a)
13.9 (160.6)
Benefits Paid(60.9)(58.9)
Participant Contributions6.6 10.2 
Obligation, End of Year$746.3 $739.7 
Change in Plan Assets  
Fair Value, Beginning of Year$568.6 $745.7 
Actual Return on Plan Assets55.1 (130.5)
Employer Contribution (b)
26.2 12.3 
Benefits Paid(60.9)(58.9)
Fair Value, End of Year$589.0 $568.6 
Funded Status, End of Year$(157.3)$(171.1)
Net Pension Amounts Recognized in Consolidated Balance Sheet Consist of:  
Current Liabilities$(2.1)$(2.1)
Non-Current Liabilities $(155.2)$(169.0)
(a)    Actuarial gain in 2022 was primarily the result of increases in discount rates.
(b)    Includes Participant Contributions noted above, any contributions made by the Company to pension plan trusts and any direct benefit payments made under certain plans.
Postretirement Health and Life Obligation and Funded Status
As of December 3120232022
Millions  
Change in Benefit Obligation  
Obligation, Beginning of Year$110.4 $148.2 
Service Cost2.0 3.0 
Interest Cost5.6 4.4 
Actuarial Gain (a)
(9.3)(38.7)
Benefits Paid(8.1)(9.2)
Participant Contributions2.4 2.7 
Plan Amendments (b)
(29.1)— 
Obligation, End of Year$73.9 $110.4 
Change in Plan Assets  
Fair Value, Beginning of Year$162.6 $201.8 
Actual Return on Plan Assets20.3 (33.0)
Employer Contribution (Withdrawal)(3.4)0.3 
Participant Contributions2.4 2.7 
Benefits Paid(8.1)(9.2)
Fair Value, End of Year$173.8 $162.6 
Funded Status, End of Year$99.9 $52.2 
Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet Consist of:  
Non-Current Assets$106.3$58.8
Current Liabilities$(0.2)$(0.2)
Non-Current Liabilities$(6.2)$(6.4)
(a)Actuarial gain in 2022 was primarily the result of increases in discount rates.
(b)In 2023, the postretirement health care plan was amended to change the company contribution to an annual stipend for certain retirees.
Amounts Recognized in Consolidated Balance Sheet
Reconciliation of Net Pension Amounts Recognized in Consolidated Balance Sheet
As of December 3120232022
Millions  
Net Loss$(256.9)$(260.2)
Prior Service Credit0.1
Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset)99.689.0
Total Net Pension Amounts Recognized in Consolidated Balance Sheet$(157.3)$(171.1)
Reconciliation of Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet
As of December 3120232022
Millions  
Net Gain (a)
$24.8$9.2
Prior Service Credit33.813.2
Accumulated Net Periodic Benefit Cost in Excess of Contributions (a)
41.329.8
Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet$99.9$52.2
(a)Excludes gains, losses and contributions associated with irrevocable grantor trusts.
Components of Net Periodic Cost
Components of Net Periodic Pension Cost
Year Ended December 31202320222021
Millions   
Service Cost$6.5 $9.3 $11.0 
Non-Service Cost Components (a)
Interest Cost40.5 27.2 24.6 
Expected Return on Plan Assets(43.8)(41.5)(43.4)
Amortization of Loss5.8 11.4 18.8 
Amortization of Prior Service Credit(0.1)(0.1)(0.2)
Net Pension Cost$8.9 $6.3 $10.8 
(a)These components of net periodic pension cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.
Components of Net Periodic Postretirement Health and Life Cost
Year Ended December 31202320222021
Millions   
Service Cost$2.0 $3.0 $3.6 
Non-Service Cost Components (a)
Interest Cost5.6 4.4 4.4 
Expected Return on Plan Assets(11.4)(9.6)(9.9)
Amortization of (Gain) Loss(2.7)0.4 3.0 
Amortization of Prior Service Credit(8.5)(7.5)(7.6)
Net Postretirement Health and Life Credit$(15.0)$(9.3)$(6.5)
(a)These components of net periodic postretirement health and life cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Other Changes in Pension Plan Assets and Benefit Obligations Recognized in
Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 3120232022
Millions  
Net Loss$2.5$11.4
Amortization of Prior Service Credit0.1 0.1 
Prior Service Credit Arising During the Period— 0.8 
Amortization of Loss(5.7)(11.4)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities$(3.1)$0.9
Other Changes in Postretirement Benefit Plan Assets and Benefit Obligations
Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 3120232022
Millions  
Net (Gain) Loss$(18.3)$3.9
Prior Service Credit Arising During the Period(29.1)— 
Amortization of Prior Service Credit8.4 7.5 
Amortization of Gain (Loss)2.7 (0.4)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities$(36.3)$11.0
Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets
Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets
As of December 3120232022
Millions  
Projected Benefit Obligation$746.3 $739.7 
Accumulated Benefit Obligation$729.5 $724.5 
Fair Value of Plan Assets$589.0 $568.6 
Unrecognized Postretirement Health and Life Costs
The postretirement health and life costs that are reported as a component within the Consolidated Balance Sheet, reflected in regulatory long-term assets or liabilities and accumulated other comprehensive income, consist of the following:

Unrecognized Postretirement Health and Life Costs
As of December 3120232022
Millions  
Net Gain$(24.8)$(9.2)
Prior Service Credit(33.8)(13.2)
Total Unrecognized Postretirement Health and Life Cost$(58.6)$(22.4)
Estimated Future Benefit Payments
Estimated Future Benefit Payments    PensionPostretirement Health and Life
Millions
2024$58.4$6.3 
2025$58.1$6.2 
2026$57.5$6.1 
2027$57.2$6.1 
2028$56.9$6.0 
Years 2029 – 2033$272.6$30.0 
Weighted Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs
Weighted Average Assumptions Used to Determine Benefit Obligation
As of December 3120232022
Discount Rate  
Pension5.39%5.70%
Postretirement Health and Life5.42%5.68%
Rate of Compensation Increase3.52%3.58%
Health Care Trend Rates
Trend Rate7.00%6.50%
Ultimate Trend Rate5.00%5.00%
Year Ultimate Trend Rate Effective20382038

Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Year Ended December 31202320222021
Discount Rate
Pension5.70%3.28%2.87%
Postretirement Health and Life5.89%3.09%2.70%
Expected Long-Term Return on Plan Assets   
Pension6.83%6.00%6.50%
Postretirement Health and Life6.33%5.41%5.85%
Rate of Compensation Increase3.58%3.58%3.62%
Plan Asset Actual and Target Allocations
Actual Plan Asset AllocationsPension
Postretirement
Health and Life (a)
 2023202220232022
Equity Securities57%46%67%66%
Fixed Income Securities40%50%33%34%
Real Estate3%4%
 100%100%100%100%
(a)Includes VEBAs and irrevocable grantor trusts.
Following are the current targeted allocations as of December 31, 2023:

Plan Asset Target Allocations    Pension
Postretirement
Health and Life (a)
Equity Securities55 %65 %
Fixed Income Securities41 %35 %
Real Estate%— 
 100 %100 %
(a)Includes VEBAs and irrevocable grantor trusts.
Recurring Fair Value Measures
 Fair Value as of December 31, 2023
Recurring Fair Value MeasuresLevel 1Level 2Level 3Total
Millions    
Assets:    
Equity Securities:    
U.S. Large-cap (a)
$83.7$83.7
U.S. Mid-cap Growth (a)
69.969.9
U.S. Small-cap (a)
46.546.5
International$134.6134.6
Fixed Income Securities (a)
215.0215.0
Cash and Cash Equivalents20.420.4
Real Estate$18.918.9
Total Fair Value of Assets$155.0$415.1$18.9$589.0
(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.
 Fair Value as of December 31, 2022
Recurring Fair Value MeasuresLevel 1Level 2Level 3Total
Millions    
Assets:    
Equity Securities:    
U.S. Large-cap (a)
— $61.2 — $61.2 
U.S. Mid-cap Growth (a)
— 40.0 — 40.0 
U.S. Small-cap (a)
— 35.4 — 35.4 
International$127.0 — — 127.0 
Fixed Income Securities (a)
— 275.3 — 275.3 
Cash and Cash Equivalents7.3 — — 7.3 
Real Estate— — $22.4 22.4 
Total Fair Value of Assets$134.3 $411.9 $22.4 $568.6 
(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.
 Fair Value as of December 31, 2023
Recurring Fair Value MeasuresLevel 1Level 2Level 3Total
Millions    
Assets:    
Equity Securities: (a)
    
U.S. Large-cap $30.0 — — $30.0 
U.S. Mid-cap Growth 28.7 — — 28.7 
U.S. Small-cap 14.9 — — 14.9 
International41.9 — — 41.9 
Fixed Income Securities:    
Mutual Funds55.1 — — 55.1 
Cash and Cash Equivalents3.2 — — 3.2 
Total Fair Value of Assets$173.8 — — $173.8 
(a)The underlying investments consist of mutual funds (Level 1).
 Fair Value as of December 31, 2022
Recurring Fair Value MeasuresLevel 1Level 2Level 3Total
Millions    
Assets:    
Equity Securities: (a)
    
U.S. Large-cap $26.7 — — $26.7 
U.S. Mid-cap Growth 25.5 — — 25.5 
U.S. Small-cap 12.7 — — 12.7 
International41.5 — — 41.5 
Fixed Income Securities:    
Mutual Funds55.5 — — 55.5 
Cash and Cash Equivalents0.7 — — 0.7 
Total Fair Value of Assets$162.6 — — $162.6 
(a)The underlying investments consist of mutual funds (Level 1). 
NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)
Fair Value (Continued)
Recurring Fair Value Measures - Activity in Level 3
Recurring Fair Value Measures 
Activity in Level 3    Real Estate
Millions 
Balance as of December 31, 2022$22.4 
Actual Return on Plan Assets(3.1)
Purchases, Sales, and Settlements – Net(0.4)
Balance as of December 31, 2023$18.9
Recurring Fair Value Measures 
Activity in Level 3   Real Estate
Millions  
Balance as of December 31, 2021$21.6 
Actual Return on Plan Assets1.0 
Purchases, Sales, and Settlements – Net(0.2)
Balance as of December 31, 2022$22.4 
Recurring Fair Value Measures
Activity in Level 3Private Equity Funds
Millions 
Balance as of December 31, 2021$2.0 
Actual Return on Plan Assets(1.5)
Purchases, Sales, and Settlements – Net(0.5)
Balance as of December 31, 2022—