Pension, Postretirement and Postemployment Benefits - Assumptions used to determine year-end Pension and Postretirement Benefit Obligation (Details)	12 Months Ended
	Dec. 27, 2020	Dec. 29, 2019
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average discount rate	2.51%	3.30%
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average discount rate	2.72%	3.46%
Health care cost trend rate assumed for next year	6.25%	6.25%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)	5.00%	5.00%