Pensions and other benefit plans - Rates Used to Develop Actuarial Present Value of Projected Benefit Obligation (Details)	12 Months Ended
	Dec. 31, 2023	Jan. 01, 2023	Jan. 02, 2022
Retirement Plans
Net Periodic Benefit Cost
Service cost discount rate	4.85%	2.46%	2.14%
Interest cost discount rate	5.25%	2.80%	2.34%
Rate of increase in compensation levels	3.71%	4.02%	4.01%
Expected long-term rate of return on plan assets	7.21%	7.25%	7.71%
Benefit Obligation
Discount rate	4.58%	5.01%	2.49%
Rate of increase in compensation levels	3.69%	4.00%	4.01%
Other Benefit Plans
Net Periodic Benefit Cost
Service cost discount rate	5.40%	2.59%	2.09%
Interest cost discount rate	5.43%	2.64%	2.33%
Rate of increase in compensation levels	4.22%	4.21%	4.25%
Benefit Obligation
Discount rate	5.11%	5.42%	2.68%
Rate of increase in compensation levels	4.22%	4.21%	4.21%