Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Pension Benefits
Net periodic benefit cost (credit)
Service cost	$ 25	$ 25	$ 75	$ 74
Interest cost	81	84	242	254
Expected return on plan assets	(127)	(123)	(380)	(368)
Amortization of net actuarial loss	34	26	102	78
Amortization of prior service cost (credit)	4	4	12	11
Net periodic benefit cost (credit)	17	16	51	49
Employer contributions	300		300
Postretirement Benefits Other Than Pensions
Net periodic benefit cost (credit)
Service cost	1	1	2	2
Interest cost	3	4	9	12
Amortization of prior service cost (credit)	(2)	(6)	(6)	(17)
Net periodic benefit cost (credit)	$ 2	$ (1)	$ 5	$ (3)