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Fair Value Measurements
 6 Months Ended
Jun. 30, 2025
Fair Value Disclosures [Abstract]  
Fair Value Measurements
9.    Fair Value Measurements
We measure certain of our assets and liabilities at fair value. Fair value represents the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.
In general, reporting entities should apply valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are developed using market data and reflect assumptions that market participants would use when pricing the asset or liability. Unobservable inputs are developed using the best information available about the assumptions that market participants would use when pricing the asset or liability.
The fair value hierarchy provides transparency regarding the inputs we use to measure fair value. We categorize each fair value measurement in its entirety into the following three levels, based on the lowest level input that is significant to the entire measurement:
•Level 1 Inputs - quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date.
•Level 2 Inputs - inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.
•Level 3 Inputs - unobservable inputs for the asset or liability.
Recurring Fair Value Measurements
As of June 30, 2025
Level 1
Level 2
Level 3
Total
ASSETS:
Cash equivalents$2.8 $— $— $2.8 
Trust assets(1)
1.1 — — 1.1 
Derivative instruments— 4.6 — 4.6 
TOTAL$3.9 $4.6 $— $8.5 
LIABILITIES:
Derivative instruments$— $19.8 $— $19.8 
TOTAL$— $19.8 $— $19.8 

Recurring Fair Value Measurements
As of December 31, 2024
Level 1
Level 2
Level 3
Total
ASSETS:
Cash equivalents$7.9 $— $— $7.9 
Trust assets(1)
0.3 — — 0.3 
Derivative instruments— 4.5 — 4.5 
TOTAL$8.2 $4.5 $— $12.7 
LIABILITIES:
Derivative instruments$— $4.4 $— $4.4 
TOTAL$— $4.4 $— $4.4 
(1)Trust assets are currently invested in money market funds. These trust assets are held to fund the non-qualified supplemental executive pension benefit obligations for certain of our officers.
The following section describes the valuation techniques or inputs for fair value measurements categorized within Level 2 of the fair value hierarchy:
Level 2 Fair Value Measurements:
Asset / LiabilityValuation TechniquesInputs
LME forward financial sales contractsDiscounted cash flowsQuoted LME forward market, Secured Overnight Financing Rate ("SOFR") discount rate
Midwest Premium ("MWP") forward financial sales contractsDiscounted cash flowsQuoted MWP forward market, SOFR discount rate
Fixed for floating swapsDiscounted cash flowsQuoted LME forward market, quoted MWP forward market
Indiana Hub power price swapsDiscounted cash flowsQuoted Indiana Hub forward market, SOFR discount rate
Heavy Fuel Oil ("HFO") price swapsDiscounted cash flowsQuoted HFO forward market
When valuing Level 3 assets and liabilities, we use certain significant unobservable inputs. Management incorporates various inputs and assumptions including forward commodity prices, commodity price volatility and macroeconomic conditions, including interest rates and discount rates. Our estimates of significant unobservable inputs are ultimately based on our estimates of risks that market participants would consider when valuing our assets and liabilities.
During the three and six months ended June 30, 2025 and 2024, there were no Level 3 assets and liabilities measured at fair value on a recurring basis.