Employee Benefit Plans - Components of Net (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	175	208	351	417
Expected return on plan assets	(343)	(296)	(687)	(593)
Amortization of prior service credit	0	0	0	0
Recognized net actuarial loss	74	72	149	145
Settlements	3	2	3	2
Net periodic (benefit) cost	(91)	(14)	(184)	(29)
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure
Service cost	24	21	48	42
Interest cost	28	34	56	68
Expected return on plan assets	(11)	(12)	(22)	(24)
Amortization of prior service credit	(2)	(2)	(4)	(5)
Recognized net actuarial loss	10	9	21	20
Settlements	0	0	0	0
Net periodic (benefit) cost	$ 49	$ 50	$ 99	$ 101