Retirement Benefits (Assumptions used to determine obligations and cost) (Details)	12 Months Ended
	Dec. 25, 2020	Dec. 27, 2019	Dec. 28, 2018
U.S. Plans
Assumptions used to determine net period benefit obligation
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.60%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	2.70%	2.80%
Assumptions used to determine net periodic benefit cost
Discount rate	3.50%	4.50%	3.90%
Rate of compensation increase	2.80%	2.80%	2.80%
Expected return on assets	6.80%	7.00%	7.10%
Non-U.S. Plans
Assumptions used to determine net period benefit obligation
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	0.40%	0.40%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	1.30%	1.30%
Assumptions used to determine net periodic benefit cost
Discount rate	0.40%	1.30%	1.00%
Rate of compensation increase	1.30%	1.40%	0.90%
Expected return on assets	1.50%	2.00%	2.00%
Postretirement Medical Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	8.00%
Assumptions used to determine net period benefit obligation
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.60%	3.40%
Assumptions used to determine net periodic benefit cost
Discount rate	3.40%	4.50%	3.90%