DIVESTITURES Narrative (Details) € in Millions, R$ in Millions, $ in Millions	3 Months Ended						9 Months Ended			12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2021 EUR (€)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 BRL (R$)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 EUR (€)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (gains) losses on sales and impairments of businesses	$ 360.0					$ 5.0	$ 367.0		$ (347.0)
Change in cumulative foreign currency translation adjustment	70.0					$ 28.0	(99.0)		$ 515.0
Kwidzyn Mill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses	794.0	€ 669.0
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Kwidzyn Mill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (gains) losses on sales and impairments of businesses	404.0
Net (gains) losses on sales and impairments of businesses, net of tax	350.0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	44.0
Net (gains) losses on sales and impairments of businesses	360.0
Gain (Loss) on Sale of Assets and Asset Impairment Charges, net of tax	(394.0)
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Olmuksan
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses							$ 81.0	€ 66.0
Net (gains) losses on sales and impairments of businesses	(6.0)			$ 123.0
Net (gains) losses on sales and impairments of businesses, net of tax	$ 0.0			123.0
Assets, Fair Value Disclosure				79.0						$ 79.0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax			$ 2.0
Change in cumulative foreign currency translation adjustment			$ 2.0
Sale of stock, percentage of ownership before transaction							90.38%	90.38%
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Brazilian Industrial Packaging
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses				58.5	R$ 330
Net (gains) losses on sales and impairments of businesses										347.0
Net (gains) losses on sales and impairments of businesses, net of tax										340.0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax										327.0
Proceeds to be received at closing				49.6	280
Deferred proceeds on disposal of business				$ 8.9	R$ 50
Number of containerboard mill to be sold				3	3
Impairment of Long-Lived Assets to be Disposed of										$ 20.0
Number of box plants to be sold				4	4