Document And Entity Information - shares shares in Millions	9 Months Ended
	Jun. 28, 2025	Aug. 06, 2025
Document Information Line Items
Entity Central Index Key	0000041719
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 28, 2025
Document Fiscal Year Focus	2025
Document Transition Report	false
Entity Address, Address Line One	9335 Harris Corners Pkwy
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Charlotte
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	28269
City Area Code	866
Local Phone Number	744-7380
Entity File Number	1-03560
Entity Registrant Name	Magnera Corporation
Entity Tax Identification Number	23-0628360
Entity Incorporation, State or Country Code	PA
Entity Information, Former Legal or Registered Name	Glatfelter Corporation
Title of 12(b) Security	Common Stock
Trading Symbol	MAGN
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		35.6
Amendment Flag	false
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--09-27
Former Address [Member]
Document Information Line Items
Entity Address, Address Line One	4350 Congress Street
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	Charlotte
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	28209