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Postretirement Plans - Summary of Fair Value by Asset Category and Level Within Fair Value Hierarchy (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Jan. 02, 2016
Jan. 03, 2015
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 1,110.8 $ 1,049.2 $ 1,103.4
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 7.2 7.6  
Voluntary Employees Beneficiary Association Plan Assets [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 13.2 13.7  
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 0.7 0.1  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Debt Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 5.3 6.0  
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 3.6 3.7  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Equity securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.6 3.7  
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 3.6 3.9  
Voluntary Employees Beneficiary Association Plan Assets [Member] | Hedge Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.6 3.9  
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 6.0 6.1  
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 0.7 0.1  
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 $ 5.3 $ 6.0