Employee Benefits - Net Periodic Benefit (Income) Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Combined Pension Plan
Components of net periodic (benefit) expense
Service cost	$ 5	$ 6
Interest cost	60	63
Expected return on plan assets	(63)	(67)
Recognition of prior service credit	0	(2)
Recognition of actuarial (gain) loss	35	28
Net periodic expense	37	28
Post-Retirement Benefit Plans
Components of net periodic (benefit) expense
Service cost	1	1
Interest cost	22	23
Recognition of prior service credit	(2)	(2)
Recognition of actuarial (gain) loss	(6)	(4)
Net periodic expense	$ 15	$ 18