Significant accounting policies - Other Intangibles (Details)	12 Months Ended
	Jan. 02, 2021
Customer relationships | Minimum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	15 years
Customer relationships | Maximum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	17 years
Technology | Minimum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	5 years
Technology | Maximum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	7 years
Computer software | Minimum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	2 years
Computer software | Maximum
Finite-Lived Intangible Assets
Finite-lived intangible asset (useful life)	6 years