Retirement Benefits - Schedule of Target Asset Allocations for ATI Pension Plan (Details) - Pension Benefits	Dec. 28, 2025
Minimum | U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	0.00%
Minimum | Fixed income and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	50.00%
Minimum | Private equity and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	0.00%
Maximum | U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	20.00%
Maximum | Fixed income and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	100.00%
Maximum | Private equity and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	40.00%