Employee Benefit Plans - Schedule of Benefit Plan Components (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	221	232	442	464
Expected return on plan assets	(220)	(207)	(440)	(414)
Amortization of prior service credit	0	0	0	0
Recognized net actuarial loss	58	33	116	67
Net periodic cost	59	58	118	117
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	16	13	32	26
Interest cost	35	39	70	78
Expected return on plan assets	(20)	(21)	(40)	(42)
Amortization of prior service credit	(7)	(7)	(14)	(14)
Recognized net actuarial loss	6	1	12	2
Net periodic cost	$ 30	$ 25	$ 60	$ 50