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Pension, Retiree Medical and Savings Plans (Level 3 Assets) (Details) | Dec. 25, 2021 | Dec. 26, 2020
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Corporate Bonds |  |
Change in fair value of plan assets |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage | 32.00% | 30.00%

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- Definition Percentage of investment to total investment within defined benefit plan asset category. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 + Details
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