Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension and Other Postretirement Benefits
Pension and other postretirement benefit contributions
Contributions to pension and other postretirement benefit plans	$ 152	$ 106
Expected full year contributions to pension and other postretirement benefit plans during the year	365
UNITED STATES
Components of net periodic benefit cost:
Service cost	32	29
Interest cost	133	131
Expected return on plan assets	(202)	(184)
Amortization of prior service cost / (credit)	0	0
Curtailments and termination benefits	0	9
Net periodic benefit cost (benefit)	$ (37)	$ (15)
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost	3.70%	4.20%
Discount rate used to measure interest cost	3.20%	3.30%
Expected rate of return on plan assets (as a percent)	6.30%	6.70%
Rate of compensation increase (as a percent)	4.00%	4.00%
Foreign Plan
Components of net periodic benefit cost:
Service cost	$ 22	$ 23
Interest cost	25	25
Expected return on plan assets	(56)	(57)
Amortization of prior service cost / (credit)	0	0
Curtailments and termination benefits	0	20
Net periodic benefit cost (benefit)	$ (9)	$ 11
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost	2.30%	2.30%
Discount rate used to measure interest cost	2.20%	2.30%
Expected rate of return on plan assets (as a percent)	5.20%	5.90%
Rate of compensation increase (as a percent)	4.00%	4.00%
Other Postretirement Benefits Plan
Components of net periodic benefit cost:
Service cost	$ 21	$ 19
Interest cost	31	33
Expected return on plan assets	(8)	(9)
Amortization of prior service cost / (credit)	(9)	(5)
Curtailments and termination benefits	0	0
Net periodic benefit cost (benefit)	$ 35	$ 38
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost	3.50%	3.90%
Discount rate used to measure interest cost	3.20%	3.30%
Expected rate of return on plan assets (as a percent)	7.50%	7.50%
Rate of compensation increase (as a percent)	4.60%	4.00%