Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017
Defined Benefit Plan Disclosure [Line Items]
Required employer contributions to defined-benefit retirement plans during the fiscal year	$ 315		$ 315
Additional discretionary contributions made by employer to defined benefit plan	255
Expected future employer contributions to defined-benefit retirement plans during the fiscal year	570		570
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	45	$ 42	135	$ 126
Interest cost	140	113	394	339
Expected return on plan assets	(225)	(169)	(632)	(508)
Recognized net actuarial loss (gain)	94	86	283	258
Amortization of prior service credit	(11)	(17)	(33)	(50)
Net periodic benefit cost (credit)	43	55	147	165
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	8	9
Interest cost	8	8	24	25
Expected return on plan assets	(10)	(8)	(29)	(25)
Recognized net actuarial loss (gain)	(1)	(1)	(3)	(3)
Amortization of prior service credit	(1)	(1)	(3)	(3)
Net periodic benefit cost (credit)	$ (1)	$ 1	$ (3)	$ 3