Employee Benefit Plans - Schedule of Benefit Plan Components (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	213	229	426	458
Expected return on plan assets	(286)	(226)	(572)	(452)
Amortization of prior service credit	0	0	0	0
Recognized net actuarial loss	66	59	132	118
Net (benefit) cost	(7)	62	(14)	124
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	22	17	44	34
Interest cost	35	37	70	74
Expected return on plan assets	(17)	(18)	(34)	(36)
Amortization of prior service credit	(7)	(7)	(14)	(14)
Recognized net actuarial loss	8	6	16	12
Net (benefit) cost	$ 41	$ 35	$ 82	$ 70