Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Contributions - Defined benefit plans	$ 46	$ 75
Contributions - Defined contribution plans	90	78
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	93	94
Interest cost	278	302
Expected return on plan assets	540	556
Amortization of prior service credit	(9)	(8)
Recognized actuarial net loss (gain)	(143)	(135)
Net settlement and curtailment loss	(1)	(12)
Total net periodic benefit (income) cost	(34)	(21)
Defined Benefit Plan, Effect of Plan Amendment on Accumulated Benefit Obligation	170
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	7	8
Expected return on plan assets	0	0
Amortization of prior service credit	0	0
Recognized actuarial net loss (gain)	3	1
Net settlement and curtailment loss	0	0
Total net periodic benefit (income) cost	$ 5	$ 8