Accumulated Other Comprehensive Income (Loss) (Details2) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Oct. 01, 2023	Jul. 02, 2023	Apr. 02, 2023	Jan. 01, 2023	Oct. 02, 2022	Jul. 03, 2022	Apr. 03, 2022	Dec. 31, 2023	Jan. 01, 2023	Jan. 02, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits									$ (0.6)	$ (0.5)	$ (1.8)
Amortization of net actuarial loss									6.0	13.2	13.9
Settlement gain (loss)									(1.1)	(0.7)	21.9
Cost of sales									(3,371.1)	(3,121.8)	(2,466.6)
Income (loss) before income taxes									295.2	354.6	233.4
Income tax provision (benefit)									(128.2)	15.5	26.8
Reclassification adjustment included in net income									0.0	20.0	0.0
Revenue from Contract with Customer, Excluding Assessed Tax	$ (1,064.0)	$ (1,025.6)	$ (1,046.0)	$ (1,038.1)	$ (1,010.4)	$ (1,032.0)	$ (959.5)	$ (834.1)	(4,173.7)	(3,836.0)	(2,799.8)
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)	(0.9)
Amortization of net actuarial loss									6.0	13.2
Settlement gain (loss)									0.0	0.0
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									0.6	0.5	1.8
Amortization of net actuarial loss									(6.0)	(13.2)	(13.9)
Settlement gain (loss)									(1.1)	(0.7)	21.9
Income (loss) before income taxes									(6.5)	(13.4)	9.8
Income tax provision (benefit)									(1.4)	(2.8)	6.2
Income (loss)									(5.1)	(10.6)	3.6
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									0.0	(20.0)	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									(2.5)	42.8	11.4
Income tax provision (benefit)									(0.6)	10.2	2.7
Income (loss)									(1.9)	32.6	8.7
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									3.3	26.9	7.1
Revenue from Contract with Customer, Excluding Assessed Tax									3.3	26.9	7.1
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									(7.5)	15.1	5.3
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									0.3	0.9	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									$ 1.4	$ (0.1)	$ (1.1)