Employee Benefits - Components of Plan Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Apr. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 22	$ 25		$ 44	$ 50
Interest cost	41	42		83	83
Expected return on plan assets	(90)	(90)		(182)	(180)
Amortization of unrecognized prior service (gain)	2	2		4	4
Recognized net (gain) loss	(2)	(2)	$ 3	(11)	1
Net periodic benefit cost	(27)	(23)		(62)	(42)
Curtailment (gain) loss	0	(3)	1	0	(2)
Total plan benefit (income) expense	(27)	(26)		(62)	(44)
Other Nonpension Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4		9	9
Interest cost	9	9		18	18
Expected return on plan assets	(23)	(25)		(47)	(49)
Amortization of unrecognized prior service (gain)	(2)	(2)		(4)	(4)
Recognized net (gain) loss	0	0	(29)	0	(29)
Net periodic benefit cost	(12)	(14)		(24)	(55)
Curtailment (gain) loss	0	0	$ 3	0	3
Total plan benefit (income) expense	(12)	(14)		(24)	(52)
Postemployment
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2		2	3
Interest cost	0	1		0	2
Recognized net (gain) loss	(1)	0		(2)	1
Total plan benefit (income) expense	$ 0	$ 3		$ 0	$ 6