Retirement Plans - Net periodic benefit cost (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 04, 2020	Mar. 30, 2019
Pension Benefits
Net periodic benefit cost
Service cost	$ 26	$ 23
Interest cost	73	82
Expected return on plan assets	(144)	(139)
Amortization of net actuarial loss	46	25
Amortization of prior service cost	3	3
Net periodic benefit cost (credit)	4	(6)
Postretirement Benefits Other Than Pensions
Net periodic benefit cost
Service cost	1	1
Interest cost	2	2
Amortization of prior service cost	(1)	(2)
Net periodic benefit cost (credit)	$ 2	$ 1