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Postretirement Plans - Summary of Target Allocation and Weighted-Average Asset Allocation by Asset Category and Fair Value of Plan Assets (Detail) - USD ($) $ in Millions | Dec. 30, 2017 | Dec. 31, 2016 | Jan. 02, 2016
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 1,305.0 | $ 1,110.8 | $ 1,049.2
Voluntary Employees Beneficiary Association Plan Assets [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation | 100.00% |  |
Actual weighted-average asset allocation | 100.00% | 100.00% |
Fair value of plan assets | $ 13.4 | $ 13.2 |
Voluntary Employees Beneficiary Association Plan Assets [Member] | Debt Securities and Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation | 46.00% |  |
Actual weighted-average asset allocation | 42.00% | 45.00% |
Voluntary Employees Beneficiary Association Plan Assets [Member] | Equity securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation | 29.00% |  |
Actual weighted-average asset allocation | 29.00% | 28.00% |
Fair value of plan assets | $ 3.8 | $ 3.6 |
Voluntary Employees Beneficiary Association Plan Assets [Member] | Hedge Funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation | 25.00% |  |
Actual weighted-average asset allocation | 29.00% | 27.00% |
Fair value of plan assets | $ 3.9 | $ 3.6 |

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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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