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Retirement Plans (Summary of Net Pension and Supplemental Executive Retirement Plan Expense Recognized) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jul. 01, 2017
Jun. 18, 2016
Jul. 01, 2017
Jun. 18, 2016
Compensation and Retirement Disclosure [Abstract]        
Service cost pertaining to benefits earned during the period $ 1.8 $ 1.5 $ 3.6 $ 3.0
Interest cost on projected benefit obligations 4.4 4.4 8.8 8.8
Expected return on pension assets (4.9) (4.7) (9.8) (9.3)
Net amortization loss 2.5 1.2 4.9 2.3
Net pension expense $ 3.8 $ 2.4 $ 7.5 $ 4.8