Derivative Instruments FV by Balance Sheet Line (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Derivatives, Fair Value [Line Items]
Derivative asset	$ 79.3	$ 0.0
Derivative liability	42.8	$ 0.0
Forward natural gas contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:DerivativeAssetsCurrent
Derivatives, Fair Value [Line Items]
Derivative asset	66.5
Forward natural gas contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent
Derivatives, Fair Value [Line Items]
Derivative asset	1.3
Forward natural gas contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesCurrent
Derivatives, Fair Value [Line Items]
Derivative liability	18.0
Forward natural gas contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Derivatives, Fair Value [Line Items]
Derivative liability	6.7
NYMEX/ICE Natural Gas Contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:DerivativeAssetsCurrent
Derivatives, Fair Value [Line Items]
Derivative asset	11.4
NYMEX/ICE Natural Gas Contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent
Derivatives, Fair Value [Line Items]
Derivative asset	0.1
NYMEX/ICE Natural Gas Contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesCurrent
Derivatives, Fair Value [Line Items]
Derivative liability	16.0
NYMEX/ICE Natural Gas Contracts \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Derivatives, Fair Value [Line Items]
Derivative liability	$ 2.1

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

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