Debt - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 28, 2025	Dec. 29, 2024	Dec. 31, 2023	Dec. 15, 2025	Jun. 13, 2025
Debt Instrument [Line Items]
Interest expense	$ 110.7	$ 124.2	$ 105.8
Interest costs capitalized	10.6	11.8	13.5
Interest and commitment fees paid	117.8	131.4	114.7
Net interest expense includes interest income	12.1	16.0	$ 13.0
2026	31.6
2027	378.6
2028	23.6
2029	343.7
2030	633.4
Allegheny Ludlum 6.95% Debentures due 2025
Debt Instrument [Line Items]
Debt instrument carrying amount	$ 0.0	150.0		$ 150.0
Interest rate	6.95%			6.95%
Credit Facility | Secured Debt | Line of Credit
Debt Instrument [Line Items]
Debt instrument carrying amount	$ 200.0	$ 200.0
Line of credit maximum borrowing capacity					$ 200.0