Postretirement Plans (Reconciliation Of Level 3 Assets Held) (Details) - Pension Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	$ 61,711	$ 56,102
Net Realized and Unrealized Gains/(Losses)	9,275	10,851
Net Purchases, Issuances and Settlements	(68)	(756)
Ending balance at fair value	68,696	61,711
Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	472	318
Net Realized and Unrealized Gains/(Losses)	2	11
Net Purchases, Issuances and Settlements	(71)	141
Net Transfers Into/(Out of) Level 3	(163)	2
Ending balance at fair value	240	472
Debt Securities [Member] | Corporate Debt Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	19,341
Ending balance at fair value	20,841	19,341
Debt Securities [Member] | Corporate Debt Securities [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	5	2
Net Realized and Unrealized Gains/(Losses)	1
Net Purchases, Issuances and Settlements	18	3
Net Transfers Into/(Out of) Level 3	16
Ending balance at fair value	40	5
Debt Securities [Member] | US Treasury and Government [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	5,759
Ending balance at fair value	5,170	5,759
Debt Securities [Member] | US Treasury and Government [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Net Transfers Into/(Out of) Level 3	2
Ending balance at fair value	2
Debt Securities [Member] | Mortgage backed and asset backed securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	1,181
Ending balance at fair value	786	1,181
Debt Securities [Member] | Mortgage backed and asset backed securities [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	461	312
Net Realized and Unrealized Gains/(Losses)	(1)	11
Net Purchases, Issuances and Settlements	(93)	137
Net Transfers Into/(Out of) Level 3	(247)	1
Ending balance at fair value	120	461
Debt Securities [Member] | Municipal [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	1,317
Ending balance at fair value	1,176	1,317
Debt Securities [Member] | Municipal [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Net Realized and Unrealized Gains/(Losses)	3
Net Purchases, Issuances and Settlements	2
Net Transfers Into/(Out of) Level 3	67
Ending balance at fair value	72
Debt Securities [Member] | Sovereign Debt Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	1,076
Ending balance at fair value	1,040	1,076
Debt Securities [Member] | Sovereign Debt Securities [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Net Realized and Unrealized Gains/(Losses)	(1)
Net Purchases, Issuances and Settlements	2
Net Transfers Into/(Out of) Level 3	1
Ending balance at fair value	2
Debt Securities [Member] | Other Debt Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	55
Ending balance at fair value	19	55
Real estate and real assets [Member] | Real assets [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	810
Ending balance at fair value	786	810
Real estate and real assets [Member] | Real assets [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	4	4
Net Purchases, Issuances and Settlements
Net Transfers Into/(Out of) Level 3	(2)
Ending balance at fair value	$ 2	$ 4