Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 26,921	$ 25,755
Other comprehensive income, net of income taxes	2	14
Ending balance	27,607	26,061
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(765)	(723)
OCI before reclassifications	5	(24)
Amounts reclassified from AOCI	5	5
Other comprehensive income, net of income taxes	10	(19)
Ending balance	(755)	(742)
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(720)	(726)
OCI before reclassifications	(1)	10
Amounts reclassified from AOCI	3	4
Other comprehensive income, net of income taxes	2	14
Ending balance	(718)	(712)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	45	(3)
OCI before reclassifications	(6)	34
Amounts reclassified from AOCI	(2)	(1)
Other comprehensive income, net of income taxes	(8)	33
Ending balance	$ 37	$ 30