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Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2025

Fair Value Disclosures [Abstract]

Schedule of financial assets and liabilities at fair value on a recurring basis

Recurring Fair Value Measurements						As of September 30, 2025
						Level 1						Level 2						Level 3						Total
ASSETS:
Cash equivalents						$	124.8					$	—					$	—					$	124.8
Trust assets(1)						0.6						—						—						0.6
Derivative instruments						—						5.2						—						5.2
TOTAL						$	125.4					$	5.2					$	—					$	130.6
LIABILITIES:
Derivative instruments						$	—					$	41.5					$	—					$	41.5
TOTAL						$	—					$	41.5					$	—					$	41.5

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.

Schedule of valuation methodology for assets and liabilities at fair value

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 / Liability

Valuation Techniques

Inputs

LME forward financial sales contracts

Discounted cash flows

Quoted LME forward market, Secured Overnight Financing Rate ("SOFR") discount rate

Midwest Premium ("MWP") forward financial sales contracts

Discounted cash flows

Quoted MWP forward market, SOFR discount rate

Fixed for floating swaps

Discounted cash flows

Quoted LME forward market, quoted MWP forward market

Indiana Hub power price swaps

Discounted cash flows

Quoted Indiana Hub forward market, SOFR discount rate

Heavy Fuel Oil ("HFO") price swaps

Discounted cash flows

Quoted HFO forward market

X

- Definition

Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 103
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-103

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

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- Definition

Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

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