Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Components of net periodic cost
Remeasurement gains and losses	$ (125)	$ 7	$ (140)	$ (7)
Pension benefits
Components of net periodic cost
Service cost	28	28	56	56
Interest cost	62	63	127	124
Expected return on plan assets	(101)	(107)	(194)	(220)
Amortization of prior service credit	(14)	(14)	(28)	(28)
Costs and expenses	(25)	(30)	(39)	(68)
Remeasurement of projected benefit obligation	344	(86)	731	(276)
Remeasurement of plan assets	(225)	85	(616)	297
Remeasurement gains and losses	(119)	1	(115)	(21)
Total net cost (benefit)	94	(31)	76	(47)
Postretirement benefits
Components of net periodic cost
Service cost	2	2	4	4
Interest cost	3	3	7	7
Amortization of prior service credit	(1)	(6)	(2)	(11)
Costs and expenses	4	(1)	9	0
Remeasurement of projected benefit obligation	6	(6)	25	(14)
Remeasurement of plan assets	0	0	0	0
Remeasurement gains and losses	(6)	6	(25)	14
Total net cost (benefit)	$ 10	$ (7)	$ 34	$ (14)