Postretirement Plans - Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets (Details) - Pension - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	$ 48,891	$ 49,825
Net Realized and Unrealized Gains/(Losses)	738	3,756
Ending balance at fair value	45,574	48,891
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	226	268
Net Realized and Unrealized Gains/(Losses)	(3)	14
Net Purchases, Issuances and Settlements	(15)	(12)
Net Transfers Into/(Out of) Level 3	5	(44)
Ending balance at fair value	213	226
Fixed income | Corporate
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	17,809
Ending balance at fair value	16,322	17,809
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	59	70
Net Realized and Unrealized Gains/(Losses)	(3)	5
Net Purchases, Issuances and Settlements	(22)	(16)
Net Transfers Into/(Out of) Level 3
Ending balance at fair value	34	59
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	6,822
Ending balance at fair value	5,182	6,822
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
Net Realized and Unrealized Gains/(Losses)
Net Purchases, Issuances and Settlements		(1)
Net Transfers Into/(Out of) Level 3		1
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	505
Ending balance at fair value	783	505
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	161	162
Net Realized and Unrealized Gains/(Losses)	2	7
Net Purchases, Issuances and Settlements	5	10
Net Transfers Into/(Out of) Level 3	4	(18)
Ending balance at fair value	172	161
Fixed income | Municipal
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	816
Ending balance at fair value	613	816
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		32
Net Realized and Unrealized Gains/(Losses)
Net Purchases, Issuances and Settlements		(5)
Net Transfers Into/(Out of) Level 3		(27)
Ending balance at fair value
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 Gains/(Losses)	(3)	3
Net Purchases, Issuances and Settlements
Net Transfers Into/(Out of) Level 3
Ending balance at fair value		3
Fixed income | Sovereign
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance at fair value	720
Ending balance at fair value	924	720
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
Net Realized and Unrealized Gains/(Losses)
Net Purchases, Issuances and Settlements	1
Net Transfers Into/(Out of) Level 3
Ending balance at fair value	1
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
Net Realized and Unrealized Gains/(Losses)
Net Purchases, Issuances and Settlements	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	2,204
Ending balance at fair value	2,530	2,204
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 Gains/(Losses)	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	3	4
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	$ 3