Post-retirement benefits - Schedule of major assumptions used (Details)	12 Months Ended
Jan. 01, 2022	Jan. 02, 2021
Pensions
Benefit obligation:
Discount rate (percentage)	2.003%	1.527%
Rate of salary increase (percentage)	3.095%	3.032%
Net periodic benefit cost:
Discount rate (percentage)	1.527%	2.144%
Rate of salary increase (percentage)	3.032%	3.17%
Expected return on plan assets (percentage)	2.38%	2.832%
Other post-retirement benefits
Benefit obligation:
Discount rate (percentage)	2.81%	2.30%
Net periodic benefit cost:
Discount rate (percentage)	2.30%	3.08%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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