Postretirement Plans - Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets (Details) - Pension - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	$ 45,574	$ 48,891
Net Realized and Unrealized (Losses)/Gains	4,562	738
Ending balance at fair value	47,147	45,574
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	213	226
Net Realized and Unrealized (Losses)/Gains	6	(3)
Net Purchases, Issuances and Settlements	306	(15)
Net Transfers Into/(Out of) Level 3	(30)	5
Ending balance at fair value	495	213
Fixed income | Corporate
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	16,322
Ending balance at fair value	15,774	16,322
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	34	59
Net Realized and Unrealized (Losses)/Gains	3	(3)
Net Purchases, Issuances and Settlements	246	(22)
Net Transfers Into/(Out of) Level 3	(30)
Ending balance at fair value	253	34
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	5,182
Ending balance at fair value	5,908	5,182
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	783
Ending balance at fair value	646	783
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	172	161
Net Realized and Unrealized (Losses)/Gains	3	2
Net Purchases, Issuances and Settlements	11	5
Net Transfers Into/(Out of) Level 3		4
Ending balance at fair value	186	172
Fixed income | Municipal
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	613
Ending balance at fair value	524	613
Fixed income | Other | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value		3
Net Realized and Unrealized (Losses)/Gains		(3)
Net Purchases, Issuances and Settlements
Net Transfers Into/(Out of) Level 3
Ending balance at fair value
Fixed income | Sovereign
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	924
Ending balance at fair value	2,055	924
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	1
Net Realized and Unrealized (Losses)/Gains
Net Purchases, Issuances and Settlements	1	1
Net Transfers Into/(Out of) Level 3
Ending balance at fair value	2	1
Fixed income | Asset backed private loans
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Ending balance at fair value	54
Fixed income | Asset backed private loans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value
Net Realized and Unrealized (Losses)/Gains
Net Purchases, Issuances and Settlements	54
Net Transfers Into/(Out of) Level 3
Ending balance at fair value	54
Fixed income | Cash equivalents and other short-term investments | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	4
Net Realized and Unrealized (Losses)/Gains
Net Purchases, Issuances and Settlements	(4)	4
Net Transfers Into/(Out of) Level 3
Ending balance at fair value		4
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	2,530
Ending balance at fair value	2,464	2,530
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
Net Realized and Unrealized (Losses)/Gains		1
Net Purchases, Issuances and Settlements		(1)
Net Transfers Into/(Out of) Level 3
Ending balance at fair value
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	3
Net Realized and Unrealized (Losses)/Gains
Net Purchases, Issuances and Settlements	(2)	(2)
Net Transfers Into/(Out of) Level 3		1
Ending balance at fair value		$ 2