Employee Benefit Plans - Net Periodic Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0
Interest cost	917	884	928
Expected return on plan assets	(902)	(879)	(829)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss	233	232	134
Settlements	3	3	0
Net periodic cost	251	240	233
Defined contribution plan costs	733	592	551
Total cost	984	832	784
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	68	62	52
Interest cost	147	141	155
Expected return on plan assets	(74)	(81)	(84)
Amortization of prior service credit	(26)	(26)	(26)
Recognized net actuarial loss	24	24	4
Settlements	0	0	0
Net periodic cost	139	120	101
Defined contribution plan costs	0	0	0
Total cost	$ 139	$ 120	$ 101