Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined benefit pension plans, U.S.
Amortization:
Total defined contribution plans	$ 449	$ 438	$ 447
Pension plans, Non-U.S.
Amortization:
Total defined contribution plans	320	329	321
Defined benefit pension plans, U.S.
Components of net periodic benefit cost [Abstract]
Benefits earned during the year	340	281	314
Interest cost on benefit obligations	498	534	447
Expected return on plan assets	(929)	(985)	(956)
Amortization:
Net (gain)/loss	247	25	271
Prior service cost/(credit)	(34)	(41)	(41)
Special termination benefits	0	0	0
Net periodic defined benefit cost	122	(186)	35
Other defined benefit pension plans	14	14	15
Total defined benefit plans	136	(172)	50
Total pension and OPEB cost included in compensation expense	585	266	497
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net (gain)/loss arising during the year	(3)	1,645	(1,817)
Prior service credit arising during the year	0	53	0
Amortization of net loss	(247)	(25)	(271)
Amortization of prior service (cost)/credit	34	41	41
Foreign exchange impact and other	0	0	0
Total recognized in other comprehensive income	(216)	1,714	(2,047)
Total recognized in net periodic benefit cost and other comprehensive income	(94)	1,528	(2,012)
Pension plans, Non-U.S.
Components of net periodic benefit cost [Abstract]
Benefits earned during the year	37	33	34
Interest cost on benefit obligations	112	137	125
Expected return on plan assets	(150)	(172)	(142)
Amortization:
Net (gain)/loss	35	47	49
Prior service cost/(credit)	(2)	(2)	(2)
Special termination benefits	1	0	0
Net periodic defined benefit cost	33	43	64
Other defined benefit pension plans	10	6	14
Total defined benefit plans	43	49	78
Total pension and OPEB cost included in compensation expense	363	378	399
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net (gain)/loss arising during the year	(47)	57	19
Prior service credit arising during the year	0	0	0
Amortization of net loss	(35)	(47)	(49)
Amortization of prior service (cost)/credit	2	2	2
Foreign exchange impact and other	(33)	(39)	14
Total recognized in other comprehensive income	(113)	(27)	(14)
Total recognized in net periodic benefit cost and other comprehensive income	(80)	16	50
OPEB plans
Components of net periodic benefit cost [Abstract]
Benefits earned during the year	1	0	1
Interest cost on benefit obligations	31	38	35
Expected return on plan assets	(106)	(101)	(92)
Amortization:
Net (gain)/loss	0	0	1
Prior service cost/(credit)	0	(1)	0
Special termination benefits	0	0	0
Net periodic defined benefit cost	(74)	(64)	(55)
Total defined benefit plans	(74)	(64)	(55)
Total pension and OPEB cost included in compensation expense	(74)	(64)	(55)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net (gain)/loss arising during the year	21	(5)	(257)
Prior service credit arising during the year	0	0	0
Amortization of net loss	0	0	(1)
Amortization of prior service (cost)/credit	0	1	0
Foreign exchange impact and other	0	0	0
Total recognized in other comprehensive income	21	(4)	(258)
Total recognized in net periodic benefit cost and other comprehensive income	$ (53)	$ (68)	$ (313)