Employee Benefits - Net Periodic Benefit (Income) Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Combined Pension Plan
Components of net periodic (benefit) expense
Service cost	$ 6	$ 7	$ 18	$ 19
Interest cost	63	67	188	202
Expected return on plan assets	(68)	(72)	(204)	(215)
Recognition of prior service credit	(3)	(2)	(6)	(5)
Recognition of actuarial (gain) loss	28	27	82	78
Net periodic post-retirement benefit expense	26	27	78	79
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	1	1	3	4
Interest cost	23	26	70	77
Recognition of prior service credit	(1)	(2)	(5)	(6)
Recognition of actuarial (gain) loss	(4)	(5)	(13)	(15)
Special termination benefits charge	0	0	2	0
Net periodic post-retirement benefit expense	$ 19	$ 20	$ 57	$ 60