Employee Benefits - Net Periodic Benefit (Income) Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Combined Pension Plan
Components of net periodic (benefit) expense
Service cost	$ 6	$ 6	$ 12	$ 12
Interest cost	62	67	125	135
Expected return on plan assets	(69)	(72)	(136)	(143)
Recognition of prior service credit	(1)	(1)	(3)	(3)
Recognition of actuarial (gain) loss	26	26	54	51
Net periodic post-retirement benefit expense	24	26	52	52
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	1	2	2	3
Interest cost	24	25	47	51
Recognition of prior service credit	(2)	(2)	(4)	(4)
Recognition of actuarial (gain) loss	(5)	(5)	(9)	(10)
Special termination benefits charge	2	0	2	0
Net periodic post-retirement benefit expense	$ 20	$ 20	$ 38	$ 40