Pension and postretirement benefits - Contributions to Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 28, 2024	Sep. 30, 2023	Sep. 28, 2024	Sep. 30, 2023	Dec. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to employee benefit plans	$ 7	$ 0	$ 17	$ 1	$ 0
Total current year projected employer contributions	24		24
Expected future employer contributions, next fiscal year					24
Previously Reported
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year					0
Pension
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to employee benefit plans	7	0	17	1	0
Total current year projected employer contributions	24		24
Nonpension postretirement
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to employee benefit plans	0	$ 0	0	$ 0	$ 0
Total current year projected employer contributions	$ 0		$ 0