Pension and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits, U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 282	$ 307	$ 300
Interest cost	456	434	425
Expected return on plan assets	(831)	(819)	(782)
Net amortization	64	158	74
Termination benefits	23	22	53
Curtailments	5	(12)	(69)
Settlements	0	1	11
Net periodic benefit (credit) cost	(1)	91	12
Pension Benefits, International
Defined Benefit Plan Disclosure [Line Items]
Service cost	238	251	266
Interest cost	204	206	269
Expected return on plan assets	(382)	(379)	(416)
Net amortization	76	104	59
Termination benefits	4	1	11
Curtailments	(1)	(9)	(4)
Settlements	6	12	6
Net periodic benefit (credit) cost	145	186	191
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	54	80	78
Interest cost	82	110	115
Expected return on plan assets	(107)	(143)	(139)
Net amortization	(103)	(59)	(71)
Termination benefits	4	7	22
Curtailments	(18)	(19)	(39)
Settlements	0	0	0
Net periodic benefit (credit) cost	$ (88)	$ (24)	$ (34)