Benefit Plans (Schedule of Components of Net Periodic Pension 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	$ 70	$ 81	$ 75
Interest cost	306	276	288
Expected return on plan assets	(576)	(585)	(601)
Amortization of net loss	159	225	197
Amortization of prior service cost (credit)	6	4	4
Settlement and curtailment	27	16	86
Net periodic benefit cost (income)	(8)	17	49
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	16	18	16
Interest cost	76	70	76
Expected return on plan assets	(15)	(19)	0
Amortization of net loss	5	21	25
Amortization of prior service cost (credit)	(30)	(42)	(38)
Settlement and curtailment	5	0	0
Net periodic benefit cost (income)	$ 57	$ 48	$ 79