Benefit Plans (Schedule of Components of Net Periodic Pension Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 81	$ 75	$ 76
Interest cost	276	288	281
Expected return on plan assets	(585)	(601)	(553)
Amortization of net loss	225	197	171
Amortization of prior service cost (credit)	4	4	5
Termination, settlement and curtailment	16	86	34
Net periodic benefit cost	17	49	14
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	18	16	17
Interest cost	70	76	77
Expected return on plan assets	(19)	0	0
Amortization of net loss	21	25	25
Amortization of prior service cost (credit)	(42)	(38)	(39)
Termination, settlement and curtailment	0	0	(2)
Net periodic benefit cost	$ 48	$ 79	$ 78