Equity Method Investments (Narrative) (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2018	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Proceeds from sales of equity method investments				$ 500	$ 0	$ 0
Equity earnings (loss), net of taxes				77	250	336
Equity method dividends received				$ 162	273	153
Reportable Subsegments [Member] | Ilim Holding [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest				50.00%
Equity earnings (loss), net of taxes				$ 48	207	290
Equity method dividends received				141	246
Equity method investments				393	508
Equity method investment, difference between carrying amount and underlying equity				127	136
Foreign currency transaction gain (loss), net of tax				(50)	32	(82)
Purchases from related party				$ 174	215	$ 214
Reportable Subsegments [Member] | Graphic Packaging LLC [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest				15.00%		20.50%
Equity method investment, aggregate units exchanged		15,150,784
Proceeds from exchange of aggregate units owned in an equity method investment		$ 250
Equity method investments, aggregate units exchanged	17,399,414		79,911,511
Gain (Loss) on Sale of Equity Investments		33
Gain (loss) on sale of equity method investment, net of tax		25
Proceeds from sales of equity method investments	$ 250
Equity earnings (loss), net of taxes				$ 40	46	$ 46
Equity method dividends received				20	27
Equity method investments				702	1,100
Equity method investment, difference between carrying amount and underlying equity				345	529
Revenue from related party				$ 253	$ 274	$ 240
Graphic Packaging LLC [Member] | Reportable Subsegments [Member]
Schedule of Equity Method Investments [Line Items]
Gain (Loss) on Sale of Equity Investments		$ 33