Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net periodic cost
Costs and expenses	$ (31)	$ (9)
Remeasurement (gains) losses	318	15
Total net cost	287	6
Pension benefits
Components of net periodic cost
Service cost	28	28
Interest cost	56	65
Expected return on plan assets	(104)	(93)
Amortization of prior service credit	(14)	(14)
Costs and expenses	(34)	(14)
Remeasurement of projected benefit obligation	(116)	387
Remeasurement of plan assets	434	(391)
Remeasurement (gains) losses	318	(4)
Total net cost	284	(18)
Postretirement benefits
Components of net periodic cost
Service cost	1	2
Interest cost	3	4
Amortization of prior service credit	(1)	(1)
Costs and expenses	3	5
Remeasurement of projected benefit obligation	0	19
Remeasurement of plan assets	0	0
Remeasurement (gains) losses	0	19
Total net cost	$ 3	$ 24