Benefit Plans (Schedule of Components of Net Periodic Pension Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 74	$ 70	$ 81
Interest cost	251	306	276
Expected return on plan assets	(502)	(576)	(585)
Amortization of net loss	134	159	225
Amortization of prior service cost (credit)	5	6	4
Settlement and curtailment	10	27	16
Net periodic benefit cost (income)	(28)	(8)	17
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	16	16	18
Interest cost	59	76	70
Expected return on plan assets	(14)	(15)	(19)
Amortization of net loss	10	5	21
Amortization of prior service cost (credit)	(30)	(30)	(42)
Settlement and curtailment	0	5	0
Net periodic benefit cost (income)	$ 41	$ 57	$ 48