Employee Benefit Plans - Net Periodic Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0
Interest cost	884	928	861
Expected return on plan assets	(879)	(829)	(734)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss	232	134	221
Settlements	3	0	6
Net periodic cost	240	233	354
Defined contribution plan costs	592	551	490
Total cost	832	784	844
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	62	52	49
Interest cost	141	155	143
Expected return on plan assets	(81)	(84)	(84)
Amortization of prior service credit	(26)	(26)	(26)
Recognized net actuarial loss	24	4	25
Settlements	0	0	0
Net periodic cost	120	101	107
Defined contribution plan costs	0	0	0
Total cost	$ 120	$ 101	$ 107