Derivatives, Hedging Programs and Other Financial Instruments, Realized and Unrealized Gains (Losses) Table (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments Gain Loss [Line Items]
Cost of products sold, excluding depreciation and amortization and other items	$ 286.6	$ 315.1
Depreciation and amortization	13.2	11.9
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	7.0	4.2
Cash Flow Hedges \| Cost of Sales \| Aluminum \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	5.7	4.2
Cash Flow Hedges \| Cost of Sales \| Alloy Metal Hedge \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	0.6	0.1
Cash Flow Hedges \| Cost of Sales \| Natural Gas \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	0.5	(0.1)
Cash Flow Hedges \| Cost of Sales \| Electricity \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	0.2	0.0
Fair Value Hedges \| Depreciation and Amortization \| Foreign Exchange Contract \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in income related to cash flow hedges:	0.2	0.0
Foreign exchange contracts	0.2	0.0
Hedged item	(0.2)	0.0
Excluded component amortized from AOCI to income	$ 0.2	$ 0.0

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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