Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 214	$ 210	$ 208
Interest cost	118	109	108
Expected return on plan assets	(328)	(349)	(326)
Amortization:
Net losses	189	172	186
Prior service cost	(1)	2	6
Settlement and curtailment	4	15	6
Net periodic pension cost	196	159	188
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	4	4
Interest cost	7	9	8
Expected return on plan assets	0	0	0
Amortization:
Net losses	0	4	5
Prior service cost	0	(1)	0
Settlement and curtailment	0	0	0
Net periodic pension cost	$ 9	$ 16	$ 17