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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