Postretirement Plans - Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets (Details) - Pension - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	$ 67,813	$ 68,696
Net Realized and Unrealized Gains/(Losses)	(13,141)	4,477
Net Purchases, Issuances and Settlements		(870)
Ending balance at fair value	49,825	67,813
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	198	240
Net Realized and Unrealized Gains/(Losses)	(90)	(7)
Net Purchases, Issuances and Settlements	31	5
Net Transfers Into/(Out of) Level 3	129	(40)
Ending balance at fair value	268	198
Real assets | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Ending balance at fair value	5
Fixed income | Corporate
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	20,573
Ending balance at fair value	15,095	20,573
Fixed income | Corporate | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	53	40
Net Realized and Unrealized Gains/(Losses)	(19)	(1)
Net Purchases, Issuances and Settlements	3	5
Net Transfers Into/(Out of) Level 3	33	9
Ending balance at fair value	70	53
Fixed income | U.S. government and agencies
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	11,285
Ending balance at fair value	7,827	11,285
Fixed income | U.S. government and agencies | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value		2
Net Realized and Unrealized Gains/(Losses)
Net Purchases, Issuances and Settlements		(2)
Net Transfers Into/(Out of) Level 3
Ending balance at fair value
Fixed income | Mortgage backed and asset backed
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	777
Ending balance at fair value	664	777
Fixed income | Mortgage backed and asset backed | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	102	120
Net Realized and Unrealized Gains/(Losses)	(11)
Net Purchases, Issuances and Settlements	16	(17)
Net Transfers Into/(Out of) Level 3	55	(1)
Ending balance at fair value	162	102
Fixed income | Municipal
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	1,064
Ending balance at fair value	843	1,064
Fixed income | Municipal | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	29	72
Net Realized and Unrealized Gains/(Losses)	(14)
Net Purchases, Issuances and Settlements	9	7
Net Transfers Into/(Out of) Level 3	8	(50)
Ending balance at fair value	32	29
Fixed income | Sovereign
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	1,135
Ending balance at fair value	706	1,135
Fixed income | Sovereign | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	9	2
Net Realized and Unrealized Gains/(Losses)		(8)
Net Purchases, Issuances and Settlements		15
Net Transfers Into/(Out of) Level 3	(9)
Ending balance at fair value		9
Global equity | Non-U.S. common and preferred stock
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	3,345
Ending balance at fair value	2,023	3,345
Global equity | Non-U.S. common and preferred stock | Level 3
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)	(45)	2
Net Purchases, Issuances and Settlements	(2)	(3)
Net Transfers Into/(Out of) Level 3	42	4
Ending balance at fair value		5
Real estate and real assets | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	784
Ending balance at fair value	362	784
Real estate and real assets | Real assets | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value		2
Net Realized and Unrealized Gains/(Losses)	(1)
Net Purchases, Issuances and Settlements	5
Net Transfers Into/(Out of) Level 3		(2)
Ending balance at fair value	$ 4