Value of input used to measure derivative asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19279-110258

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Fair Value Measurements - Significant Unobservable Inputs (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($) t MT	Dec. 31, 2021 USD ($) MT	Mar. 31, 2022 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
LME Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ (3.8)	$ (5.1)	$ (16.7)	$ (17.9)	$ (6.0)	$ 2.9
Open position to offset fixed prices (in tonnes) \| t	109,566
FX Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0.0	$ (0.2)	0.0	(0.4)	(0.2)	0.1
FX Swap [Member] \| Level 3 [Member] \| Discount rate, net [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Value/Range of Unobservable Input	0.0858	0.0858
Casthouse [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0.0	$ 0.0
Casthouse [Member] \| Level 3 [Member] \| Discount rate, net [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Value/Range of Unobservable Input	0.0858	0
Nordpool Power Price Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0.0	$ 0.2	$ 0.0	$ 1.5	$ 0.0	$ 0.0
Nordpool Power Price Swap [Member] \| Level 3 [Member] \| Discount rate, net [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Value/Range of Unobservable Input	0.0858	0.0858
Contingent Obligation [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0.0	$ 0.0
Contingent Obligation [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Open position to offset fixed prices (in tonnes) \| MT	14,000
Contingent Obligation [Member] \| Level 3 [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Open position to offset fixed prices (in tonnes) \| MT		14,000
Contingent Obligation [Member] \| Level 3 [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Open position to offset fixed prices (in tonnes) \| MT		15,000
Fixed to Variable London Metals Exchange Swap Net [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ (2.2)	$ (5.1)
Fixed to Variable London Metals Exchange Swap Net [Member] \| Level 3 [Member] \| Discount rate, net [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Value/Range of Unobservable Input	0.0858	0.0858