Postemployment Benefits Postretirement Benefit Plans - Net Cost/(Benefit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service costs/(credits)	$ (31)	$ (77)
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1
Interest cost	8	12
Expected return on plan assets	(12)	(13)
Amortization of prior service costs/(credits)	(31)	(77)
Amortization of unrecognized losses/(gains)	(3)	(2)
Net cost/(benefit)	$ (36)	$ (79)