Employee Benefits - Schedule of Net Periodic Benefit (Income) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	$ (619)	$ (686)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	56	66	$ 63
Interest cost	436	392	409
Expected return on plan assets	(618)	(685)	(666)
Special termination benefits charge	6	15	0
Recognition of prior service credit	(8)	(8)	(8)
Recognition of actuarial loss	223	178	204
Net periodic pension benefit (income) expense	95	(42)	2
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	15	18	18
Interest cost	110	97	100
Expected return on plan assets	(1)	(1)	(2)
Recognition of prior service credit	16	20	20
Net periodic pension benefit (income) expense	$ 140	$ 134	$ 136