Employee Benefit Plans - Schedule of Benefit Plan Components (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	213	229	639	687
Expected return on plan assets	(286)	(226)	(858)	(678)
Amortization of prior service credit	0	0	0	0
Recognized net actuarial loss	66	59	198	177
Net (benefit) cost	(7)	62	(21)	186
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	22	17	66	51
Interest cost	35	37	105	111
Expected return on plan assets	(17)	(18)	(51)	(54)
Amortization of prior service credit	(7)	(7)	(21)	(21)
Recognized net actuarial loss	8	6	24	18
Net (benefit) cost	$ 41	$ 35	$ 123	$ 105