Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 25,755	$ 24,744
Other comprehensive income (loss), net of income taxes	14	(1)
Ending balance	26,061	25,066
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3)	2
OCI before reclassifications	34	6
Amounts reclassified from AOCI	(1)	0
Other comprehensive income (loss), net of income taxes	33	6
Ending balance	30	8
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(723)	(640)
OCI before reclassifications	(24)	(10)
Amounts reclassified from AOCI	5	3
Other comprehensive income (loss), net of income taxes	(19)	(7)
Ending balance	(742)	(647)
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(726)	(638)
OCI before reclassifications	10	(4)
Amounts reclassified from AOCI	4	3
Other comprehensive income (loss), net of income taxes	14	(1)
Ending balance	$ (712)	$ (639)