Pensions and Other Postretirement Benefits - Benefit Cost Components (Details) - USD ($) $ in Millions	5 Months Ended	12 Months Ended
	May 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 24	$ 26	$ 25
Interest cost		107	107	108
Expected return on plan assets		(196)	(203)	(208)
Amortization of net (losses) gains		22	17	4
Amortization of prior service benefit		0	(1)	(1)
Curtailment gain	$ 0
Net cost (benefit)		(43)	(54)	(72)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		3	4	4
Interest cost		14	15	17
Expected return on plan assets		(9)	(11)	(11)
Amortization of net (losses) gains		(2)	(1)	0
Amortization of prior service benefit		(22)	(23)	(26)
Curtailment gain		0	(20)	0
Net cost (benefit)		$ (16)	$ (36)	$ (16)