Accumulated Other Comprehensive Income (Loss) (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	$ (0.5)	$ (1.8)	$ (3.1)
Amortization of net actuarial loss	76.7	89.5	85.3
Settlement gain (loss)	(29.5)	21.9	0.0
Cost of sales	(3,121.8)	(2,466.6)	(2,689.3)
Income (loss) before income taxes	162.0	10.6	(1,481.9)
Income tax provision	15.5	26.8	77.7
Reclassification adjustment included in net income (loss)	20.0	0.0	0.0
Revenue from Contract with Customer, Excluding Assessed Tax	(3,836.0)	(2,799.8)	(2,982.1)
Other Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	(0.9)	(2.4)
Amortization of net actuarial loss	13.2	13.9
Settlement gain (loss)	0.0	21.9
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	0.5	1.8	3.1
Amortization of net actuarial loss	(76.7)	(89.5)	(85.3)
Settlement gain (loss)	(29.5)	21.9	0.0
Income (loss) before income taxes	(105.7)	(65.8)	(82.2)
Income tax provision	(12.0)	(11.9)	(19.7)
Income (loss)	(93.7)	(53.9)	(62.5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Currency translation adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment included in net income (loss)	(20.0)	0.0	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes	42.8	11.4	(6.0)
Income tax provision	10.2	2.7	(1.4)
Income (loss)	32.6	8.7	(4.6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Nickel and other raw material contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	26.9	7.1	(0.8)
Revenue from Contract with Customer, Excluding Assessed Tax	26.9	7.1	(0.8)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Natural gas contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	15.1	5.3	(3.7)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Foreign Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	0.9	0.1	(0.1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	$ (0.1)	$ (1.1)	$ (1.4)