Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 28	$ 44	$ 56	$ 90
Interest cost	150	140	300	254
Expected return on plan assets	(228)	(228)	(456)	(407)
Recognized net actuarial loss (gain)	70	93	140	189
Amortization of prior service credit	(5)	(11)	(9)	(22)
Net periodic benefit cost (credit)	15	38	31	104
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	4	5
Interest cost	9	8	18	16
Expected return on plan assets	(9)	(10)	(18)	(19)
Recognized net actuarial loss (gain)	(2)	(1)	(4)	(2)
Amortization of prior service credit	(1)	(1)	(2)	(2)
Net periodic benefit cost (credit)	$ (1)	$ (2)	$ (2)	$ (2)