Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Components of net periodic cost
Costs and expenses	$ (23)	$ (25)	$ (53)	$ (93)
Remeasurement gains and losses	225	(39)	365	(32)
Total net cost (benefit)	202	(64)	312	(125)
Pension benefits
Components of net periodic cost
Service cost	30	27	86	83
Interest cost	58	65	185	189
Expected return on plan assets	(103)	(103)	(297)	(323)
Amortization of prior service credit	(14)	(14)	(42)	(42)
Costs and expenses	(29)	(25)	(68)	(93)
Remeasurement of projected benefit obligation	323	(38)	1,054	(314)
Remeasurement of plan assets	(136)	4	(752)	301
Remeasurement gains and losses	187	(34)	302	(13)
Total net cost (benefit)	158	(59)	234	(106)
Postretirement benefits
Components of net periodic cost
Service cost	2	1	6	5
Interest cost	4	4	11	11
Amortization of prior service credit	0	(5)	(2)	(16)
Costs and expenses	6	0	15	0
Remeasurement of projected benefit obligation	38	(5)	63	(19)
Remeasurement of plan assets	0	0	0	0
Remeasurement gains and losses	38	(5)	63	(19)
Total net cost (benefit)	$ 44	$ (5)	$ 78	$ (19)