Pensions and other benefit plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Jan. 01, 2023	Jan. 02, 2022
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 893	$ 1,319	$ 1,412
Interest cost	1,437	908	768
Expected return on plan assets	(2,716)	(2,756)	(2,644)
Amortization of prior service cost	(184)	(184)	(181)
Recognized actuarial losses (gains)	(199)	650	1,251
Curtailments and settlements	93	1	1
Net periodic benefit cost (credit)	(676)	(62)	607
Other Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	264	320	309
Interest cost	214	104	80
Expected return on plan assets	(7)	(8)	(7)
Amortization of prior service cost	(2)	(5)	(31)
Recognized actuarial losses (gains)	23	122	151
Curtailments and settlements	(5)	0	0
Net periodic benefit cost (credit)	$ 487	$ 533	$ 502