Employee Benefits - Net Periodic Benefit (Income) Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Combined Pension Plan
Components of net periodic (benefit) expense
Service cost	$ 6	$ 6	$ 11	$ 12
Interest cost	60	62	120	125
Expected return on plan assets	(64)	(69)	(127)	(136)
Recognition of prior service credit	(1)	(1)	(1)	(3)
Recognition of actuarial (gain) loss	37	26	72	54
Net periodic expense	38	24	75	52
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	1	1	2	2
Interest cost	22	24	44	47
Recognition of prior service credit	(1)	(2)	(3)	(4)
Recognition of actuarial (gain) loss	(7)	(5)	(13)	(9)
Special termination benefits charge	0	2	0	2
Net periodic expense	$ 15	$ 20	$ 30	$ 38