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Business Segments - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 29, 2024 | Dec. 31, 2023 | Jan. 01, 2023
Segment Reporting Information [Line Items] |  |  |
Gain (loss) on asset sales and sale of business, net | $ 52.9 | $ (0.6) | $ (105.4)
Proceeds from sales of businesses, net of transaction costs | 48.0 | (0.3) | 0.3
Restructuring and other credits (charges) | (22.1) | (31.4) | (23.7)
Total international sales | 1,836.9 | 1,922.9 | 1,617.4
Sales by U.S. operations to foreign countries | 1,425.4 | 1,498.7 | 1,217.9
Closed operations and other income (expenses) | 10.8 | (13.3) | (5.6)
Income From Government Assistance, CARES Act |  |  | 34.0
Employee retention credits | 16.7 |  |
Selling and administrative expenses | 342.3 | $ 328.1 | 297.5
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration] |  | Cost of sales |
Gains from disposal of property, plant and equipment, net | 11.6 | $ 0.3 | 0.2
Facility Closing |  |  |
Segment Reporting Information [Line Items] |  |  |
Depreciation |  | 3.8 |
Sheffield, UK Operations |  |  |
Segment Reporting Information [Line Items] |  |  |
Net gain (loss) on sale of businesses |  |  | (112.2)
Pico Rivera, CA Operations |  |  |
Segment Reporting Information [Line Items] |  |  |
Proceeds from sale of other assets |  |  | 6.2
Gain (Loss) on disposition of other assets |  |  | 6.8
Houston, PA facility |  |  |
Segment Reporting Information [Line Items] |  |  |
Gain (loss) on asset sales and sale of business, net | 2.3 |  |
Proceeds from sale of other assets | 3.5 |  |
New Bedford, MA and Remscheid, Germany |  |  |
Segment Reporting Information [Line Items] |  |  |
Net gain (loss) on sale of businesses | 52.9 |  |
Proceeds from sale of businesses, net of transaction costs | 48.0 |  |
HPMC |  |  |
Segment Reporting Information [Line Items] |  |  |
Employee Retention Credits, Aviation Manufacturing Jobs Protection Program |  |  | 27.0
Employee retention credits | 9.0 |  |
AA&S |  |  |
Segment Reporting Information [Line Items] |  |  |
Employee retention credits | $ 7.7 |  | 7.0
Allegheny & Tsingshan Stainless |  |  |
Segment Reporting Information [Line Items] |  |  |
Equity method investment ownership percentage | 50.00% |  |
Operating Segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Depreciation | $ 118.8 | 117.4 | $ 115.4
Operating Segments | Commercial Negotiations With a Customer |  |  |
Segment Reporting Information [Line Items] |  |  |
Selling and administrative expenses | 11.8 |  |
Operating Segments | HPMC | Commercial Negotiations With a Customer |  |  |
Segment Reporting Information [Line Items] |  |  |
Selling and administrative expenses | 6.3 |  |
Operating Segments | AA&S |  |  |
Segment Reporting Information [Line Items] |  |  |
Tax benefits | 22.7 | $ 10.1 |
Operating Segments | AA&S | Commercial Negotiations With a Customer |  |  |
Segment Reporting Information [Line Items] |  |  |
Selling and administrative expenses | $ 5.5 |  |
Aerospace & Defense Market Concentration Risk [Member] | Revenue Benchmark [Member] | HPMC |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of sales | 86.00% |  |
Commercial Jet Engines Concentration | Revenue Benchmark [Member] | HPMC |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of sales | 60.00% |  |
Defense Market Concentration | Revenue Benchmark [Member] | HPMC |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of sales | 10.00% |  |
Core End Markets | Revenue Benchmark [Member] | AA&S |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of sales | 60.00% |  |
Industrial Markets | Revenue Benchmark [Member] | AA&S |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of sales | 40.00% |  |
Allegheny Technologies Inc | STAL Precision Stainless Steel Company Limited [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Joint venture ownership percentage | 60.00% |  |

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