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Divestitures - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jul. 22, 2019 USD ($)	Jun. 03, 2019 USD ($) facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of facilities sold | facility							2
Proceeds from sale of businesses, net of transaction costs			$ 155.9	$ 0.0
Goodwill	$ 523.8		523.8		$ 534.7
Gain (loss) on disposal			(1.8)	$ 0.0
Forged Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received							$ 37.0
Proceeds from sale of businesses, net of transaction costs			33.0
Goodwill							$ 10.4
Gain (loss) on disposal	(0.4)	$ (7.7)	(8.1)
Prior year revenue from facilities sold					86.0
Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received						$ 127.0
Proceeds from sale of businesses, net of transaction costs			$ 122.9
Gain (loss) on disposal	6.2
Prior year revenue from facilities sold					$ 105.0
Other Asset Impairment Charges	10.2
Property, Plant and Equipment [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Asset Impairment Charges	4.5
Right of use assets, operating leases [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Asset Impairment Charges	1.4
Right of use assets, finance leases [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Asset Impairment Charges	1.0
Finite-Lived Intangible Assets [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Asset Impairment Charges	$ 3.3

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