Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 26,152	$ 25,755	$ 25,079	$ 25,066	$ 24,744	$ 25,755	$ 24,744
Other comprehensive income (loss), net of income taxes	(24)	14	34	9	(1)	(10)	42
Ending balance	26,622	26,061	25,470	25,079	25,066	26,622	25,470
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	27	(3)	17		2	(3)	2
OCI before reclassifications	(28)		22			4	37
Amounts reclassified from AOCI	(1)		(1)			(3)	(1)
Other comprehensive income (loss), net of income taxes	(29)		21			1	36
Ending balance	(2)		38	17		(2)	38
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(739)	(723)	(647)		(640)	(723)	(640)
OCI before reclassifications	0		(3)			(26)	(16)
Amounts reclassified from AOCI	5		16			15	22
Other comprehensive income (loss), net of income taxes	5		13			(11)	6
Ending balance	(734)		(634)	(647)		(734)	(634)
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(712)	(726)	(630)	(639)	(638)	(726)	(638)
OCI before reclassifications	(28)		19			(22)	21
Amounts reclassified from AOCI	4		15			12	21
Other comprehensive income (loss), net of income taxes	(24)	14	34	9	(1)	(10)	42
Ending balance	$ (736)	$ (712)	$ (596)	$ (630)	$ (639)	$ (736)	$ (596)