Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 28	$ 45	$ 84	$ 135
Interest cost	150	140	450	394
Expected return on plan assets	(228)	(225)	(684)	(632)
Recognized net actuarial loss (gain)	98	94	238	283
Amortization of prior service credit	(4)	(11)	(13)	(33)
Net periodic benefit cost (credit)	44	43	75	147
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	3	6	8
Interest cost	9	8	27	24
Expected return on plan assets	(9)	(10)	(27)	(29)
Recognized net actuarial loss (gain)	(2)	(1)	(6)	(3)
Amortization of prior service credit	(1)	(1)	(3)	(3)
Net periodic benefit cost (credit)	$ (1)	$ (1)	$ (3)	$ (3)