Postretirement Benefits (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension and Other Postretirement Benefits
Pension and other postretirement benefit contributions
Contributions to pension and other postretirement benefit plans		$ 324		$ 71	$ 522	$ 270
Expected full year contributions to pension and other postretirement benefit plans during the year		610			610
UNITED STATES
Components of net periodic benefit cost:
Service cost		29		30	87	89
Interest cost		131		129	393	388
Expected return on plan assets		(184)		(190)	(551)	(568)
Amortization of prior service cost / (credit)		0		0	0	0
Net periodic benefit cost (benefit), excluding curtailments, settlements and termination benefits		(24)		(31)	(71)	(91)
Curtailments, settlements and termination benefits		0	$ 9	0	9	0
Total cost (benefit) included in operating profit		(24)		(31)	$ (62)	$ (91)
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost					4.20%	4.50%
Discount rate used to measure interest cost					3.30%	3.40%
Expected return on plan assets (as a percent)					6.70%	6.90%
Rate of compensation increase (as a percent)					4.00%	4.00%
Foreign Plan
Components of net periodic benefit cost:
Service cost		23		22	$ 70	$ 68
Interest cost		23		30	73	90
Expected return on plan assets		(55)		(59)	(168)	(176)
Amortization of prior service cost / (credit)		0		0	(1)	0
Net periodic benefit cost (benefit), excluding curtailments, settlements and termination benefits		(9)		(7)	(26)	(18)
Curtailments, settlements and termination benefits	$ 20	0		1	20	1
Total cost (benefit) included in operating profit		(9)		(6)	$ (6)	$ (17)
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost					2.30%	2.90%
Discount rate used to measure interest cost					2.30%	2.80%
Expected return on plan assets (as a percent)					5.90%	6.10%
Rate of compensation increase (as a percent)					4.00%	3.50%
Other Postretirement Benefits Plan
Components of net periodic benefit cost:
Service cost		19		20	$ 58	$ 61
Interest cost		33		33	98	98
Expected return on plan assets		(10)		(11)	(28)	(33)
Amortization of prior service cost / (credit)		(6)		(15)	(17)	(45)
Net periodic benefit cost (benefit), excluding curtailments, settlements and termination benefits		36		27	111	81
Curtailments, settlements and termination benefits		0		0	0	(2)
Total cost (benefit) included in operating profit		$ 36		$ 27	$ 111	$ 79
Weighted-average assumptions used to determine net cost:
Discount rate used to measure service cost					3.90%	4.40%
Discount rate used to measure interest cost					3.30%	3.30%
Expected return on plan assets (as a percent)					7.50%	7.50%
Rate of compensation increase (as a percent)					4.00%	4.00%