GENERAL INFORMATION - Schedule of Accounts Receivable and Allowances (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Receivables Sold and Derecognized	$ 2,725	$ 2,687
Proceeds Collected on Behalf of Financial Institutions	2,697	2,665
Net Proceeds Paid to Financial Institutions	(42)	(32)
Deferred Purchase Price at September 30	47	35
Pledged Receivables at September 30	$ 140	$ 171

Transfer Of Financial Assets Accounted For As Sales, Amount Collected By Financial Institution

No definition available.

Name:	gpk_TransferOfFinancialAssetsAccountedForAsSalesAmountCollectedByFinancialInstitution
Namespace Prefix:	gpk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Transfer of Financial Assets Accounted For As Sales, Amount Funded by Financial Institution

+ References

No definition available.

+ Details

Name:	gpk_TransferOfFinancialAssetsAccountedForAsSalesAmountFundedByFinancialInstitution
Namespace Prefix:	gpk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Transfer Of Financial Assets Accounted For As Sales, Pledged Receivable

+ References

No definition available.

+ Details

Name:	gpk_TransferOfFinancialAssetsAccountedForAsSalesPledgedReceivable
Namespace Prefix:	gpk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Transfer of Financial Assets Accounted For As Sales, Receivable

+ References

No definition available.

+ Details

Name:	gpk_TransferOfFinancialAssetsAccountedForAsSalesReceivable
Namespace Prefix:	gpk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of derecognized financial assets from transactions which comprise an initial transfer and an agreement entered into in contemplation of the initial transfer resulting in retention of substantially all of the exposure to the economic return throughout the term of the transaction, at the date of derecognition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (a)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D

+ Details

Name:	us-gaap_TransferOfFinancialAssetsAccountedForAsSalesAmountDerecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant