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Postretirement Plans - Summary of Fair Value by Asset Category and Level Within Fair Value Hierarchy (Detail) - USD ($)
$ in Millions
Dec. 30, 2017
Dec. 31, 2016
Jan. 02, 2016
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, 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]      
Defined Benefit Plan, Fair Value of Plan Assets 13.4 13.2  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Investments Measured at NAV [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 7.7 7.2  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Cash and cash equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 0.2 0.7  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Debt Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 5.5 5.3  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Equity securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.8 3.6  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Equity securities [Member] | Investments Measured at NAV [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, 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]      
Defined Benefit Plan, Fair Value of Plan Assets 3.9 3.6  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Hedge Funds [Member] | Investments Measured at NAV [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.9 3.6  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Quoted Prices For Identical Assets (Level 1) [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 5.7 6.0  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Quoted Prices For Identical Assets (Level 1) [Member] | Cash and cash equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 0.2 0.7  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Quoted Prices For Identical Assets (Level 1) [Member] | Debt Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 5.5 $ 5.3