Accounting policies - Disaggregated net sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 29, 2024	Jul. 01, 2023	Jun. 29, 2024	Jul. 01, 2023
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 672	$ 700	$ 1,379	$ 1,420
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	588	618	1,212	1,255
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	76	72	150	146
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 8	$ 10	$ 17	$ 19