Business Segments (Details8) - USD ($)	12 Months Ended
	Dec. 31, 2023	Jan. 01, 2023	Jan. 02, 2022
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Inventory valuation reserves	$ 75,500,000	$ 70,900,000
Segment EBITDA	710,200,000	678,700,000	$ 417,100,000
Corporate expenses	(62,300,000)	(60,300,000)	(53,700,000)
Closed operations and other income (expenses)	(13,300,000)	(5,600,000)	3,100,000
Depreciation and amortization	(146,100,000)	(142,900,000)	(143,900,000)
Interest expense, net	(92,800,000)	(87,400,000)	(96,900,000)
Restructuring and other credits (charges)	(31,400,000)	(23,700,000)	10,500,000
Strike related costs	$ 0	$ 0	$ (63,200,000)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Settlement Gain (Loss), Statement Of Income Or Comprehensive Income, Extensible Enumeration, Not Disclosed Flag	Retirement benefit settlement gain (loss) (See Note 14)	Retirement benefit settlement gain (loss) (See Note 14)	Retirement benefit settlement gain (loss) (See Note 14)
Retirement benefit settlement gain (loss)	$ (41,700,000)	$ 0	$ 64,900,000
Defined Benefit Plan Net Periodic Benefit Cost Credit Immediate Recognition Of Actuarial Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag	Pension remeasurement gain (loss) (See Note 14)	Pension remeasurement gain (loss) (See Note 14)	Pension remeasurement gain (loss) (See Note 14)
Pension remeasurement gain (loss)	$ (26,800,000)	$ 100,300,000	$ 147,200,000
Joint venture restructuring credit (charge)	0	900,000	0
Debt extinguishment charge	0	0	(65,500,000)
Gain (loss) on asset sales and sale of business, net	(600,000)	(105,400,000)	13,800,000
Income (loss) before income taxes	295,200,000	354,600,000	233,400,000
Pension Benefits [Member]
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Retirement benefit settlement gain (loss)	(41,700,000)	(700,000)	0
Pension remeasurement gain (loss)	(26,800,000)	100,300,000	147,200,000
High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Strike related costs			3,500,000
Impairment of goodwill	0	0	0
Various AA&S Segment Operations
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Strike related costs			59,700,000
Operating Segments
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Depreciation and amortization	(146,100,000)	(142,900,000)	(143,900,000)
Operating Segments | High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment EBITDA	433,600,000	303,400,000	170,300,000
Depreciation and amortization	(71,100,000)	(68,300,000)	(75,000,000.0)
Operating Segments | Advanced Alloys & Solutions [Member]
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment EBITDA	276,600,000	375,300,000	246,800,000
Depreciation and amortization	$ (67,900,000)	$ (67,400,000)	$ (64,500,000)