Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of net periodic cost
Costs and expenses	$ (24)	$ (21)	$ (55)	$ (30)
Remeasurement (gains) losses	73	125	391	140
Total net cost	49	104	336	110
Pension benefits
Components of net periodic cost
Service cost	25	28	53	56
Interest cost	56	62	112	127
Expected return on plan assets	(95)	(101)	(199)	(194)
Amortization of prior service credit	(14)	(14)	(28)	(28)
Costs and expenses	(28)	(25)	(62)	(39)
Remeasurement of projected benefit obligation	672	344	556	731
Remeasurement of plan assets	(623)	(225)	(189)	(616)
Remeasurement (gains) losses	49	119	367	115
Total net cost	21	94	305	76
Postretirement benefits
Components of net periodic cost
Service cost	2	2	3	4
Interest cost	3	3	6	7
Amortization of prior service credit	(1)	(1)	(2)	(2)
Costs and expenses	4	4	7	9
Remeasurement of projected benefit obligation	24	6	24	25
Remeasurement of plan assets	0	0	0	0
Remeasurement (gains) losses	24	6	24	25
Total net cost	$ 28	$ 10	$ 31	$ 34