Employee Benefit Plans - Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0
Interest cost	833	781	853
Expected return on plan assets	(1,186)	(1,318)	(1,143)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss	291	267	262
Settlements	5	4	3
Curtailment	0	0	0
Net periodic (benefit) cost	(57)	(266)	(25)
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	83	85	87
Interest cost	137	126	138
Expected return on plan assets	(47)	(67)	(69)
Amortization of prior service credit	(9)	(24)	(26)
Recognized net actuarial loss	37	36	32
Settlements	0	0	0
Curtailment	0	(53)	0
Net periodic (benefit) cost	$ 201	$ 103	$ 162