v3.25.4

Retirement Plans and Deferred Compensation Arrangements - Schedule for Net Periodic Costs (Details) - Defined Benefit Pension Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 20	$ 11	$ 0
Interest cost	207	105	2
Expected return on assets	(272)	(142)	(2)
Amortization of:
Net actuarial (gain) loss	0	0	(1)
Prior service credit	0	0	0
Curtailment gain	0	0	0
Settlement loss	0	0	0
Net periodic benefit (income) cost	(45)	(26)	(1)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	38	32	23
Interest cost	142	112	91
Expected return on assets	(146)	(112)	(82)
Amortization of:
Net actuarial (gain) loss	34	39	33
Prior service credit	(1)	(1)	(1)
Curtailment gain	(2)	(1)	0
Settlement loss	3	20	8
Net periodic benefit (income) cost	$ 68	$ 89	$ 72

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Smurfit Westrock plc 10-K