COMMITMENTS AND CONTINGENCIES Environmental Remediation Obligations (Details) € in Millions, $ in Millions			1 Months Ended				3 Months Ended			9 Months Ended	12 Months Ended
	Jul. 29, 2025 defendant	Oct. 11, 2024 USD ($)	Jul. 31, 2024 USD ($)	Jul. 31, 2024 EUR (€)	Apr. 30, 2019 producer	Mar. 31, 2016 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 EUR (€)
Loss Contingencies [Line Items]
Liability for asbestos and environmental claims, gross							$ 276	$ 279		$ 276	$ 279
Liability for asbestos and environmental claims, net							97	100		$ 97	100
Secretariat of the Federal Revenue Bureau of Brazil
Loss Contingencies [Line Items]
Responsible party percentage										60.00%
Loss contingency accrual							48			$ 48
Income tax examination, estimate of possible loss		$ 255								389
Income tax examination, penalties and interest expense										$ 279
Responsible party percentage-Sylvamo										40.00%
Shared tax assessment payment							300			$ 300
Secretariat of the Federal Revenue Bureau of Brazil | Tax Year 2007-2015
Loss Contingencies [Line Items]
Income tax examination, estimate of possible loss										110
Artuso Pastry Foods Corp v. Packaging Corp. of America (N.D. Ill.)
Loss Contingencies [Line Items]
Loss contingency, number of defendants | defendant	12
Italian Competition Authority
Loss Contingencies [Line Items]
Loss contingency, number of defendants | producer					30
Loss contingency accrual														$ 31	€ 29
Accrual for environmental loss contingencies, period decrease			$ 6	€ 6
Cass Lake, Minnesota
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies							47	48		47	48
Kalamazoo River Superfund Site
Loss Contingencies [Line Items]
Loss contingency, damages sought, value						$ 37
Liability for asbestos and environmental claims, net, period increase (decrease)							7	27	$ 27
Liability for asbestos and environmental claims, net							27	29		27	29
Kalamazoo River Superfund Site | Georgia-Pacific Consumer Products LP, Fort James Corporation and Georgia Pacific LLC Cost Recovery Action
Loss Contingencies [Line Items]
Loss contingency, damages sought, value										79
Loss Contingency, damages awarded, value										$ 50
Loss contingencies, share of damages										15.00%
San Jacinto River Superfund Site
Loss Contingencies [Line Items]
Liability for asbestos and environmental claims, net							97	98		$ 97	98
Responsible party percentage												50.00%
San Jacinto River Superfund Site | Southern Impoundment
Loss Contingencies [Line Items]
Liability for asbestos and environmental claims, net, period increase (decrease)												$ 10
San Jacinto River Superfund Site | Northern impoundment
Loss Contingencies [Line Items]
Liability for asbestos and environmental claims, net, period increase (decrease)											27	$ 55
Versailles Pond
Loss Contingencies [Line Items]
Liability for asbestos and environmental claims, net							$ 29	$ 30		$ 29	$ 30		$ 30