Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
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-Topic 470
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Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481674/830-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

+ Details

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

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Period Type:

- Details

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Namespace Prefix:
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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpk_IncrementalTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpk_OnePointFiveOneTwoPercentSeniorNotesDueIn2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
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SUBSEQUENT EVENTS (Details) - USD ($) $ in Millions	Oct. 31, 2025	Sep. 30, 2025
Minimum \| Subsequent Event
Subsequent Event [Line Items]
Commitment fee (as a percent)	0.10%
Maximum \| Subsequent Event
Subsequent Event [Line Items]
Commitment fee (as a percent)	0.25%
Incremental Term Loan \| Subsequent Event
Subsequent Event [Line Items]
Aggregate principal amount	$ 400
1.512% Senior Notes Due In 2026 \| Senior Notes
Subsequent Event [Line Items]
Stated interest rate		1.512%
1.512% Senior Notes Due In 2026 \| Senior Notes \| Subsequent Event
Subsequent Event [Line Items]
Stated interest rate	1.512%
Senior Secured Term Loan Facilities \| Minimum \| Subsequent Event \| Secured Overnight Financing Rate (SOFR)
Subsequent Event [Line Items]
Basis spread on debt instrument (as a percent)	1.00%
Senior Secured Term Loan Facilities \| Minimum \| Subsequent Event \| Base Rate
Subsequent Event [Line Items]
Basis spread on debt instrument (as a percent)	0.00%
Senior Secured Term Loan Facilities \| Maximum \| Subsequent Event \| Secured Overnight Financing Rate (SOFR)
Subsequent Event [Line Items]
Basis spread on debt instrument (as a percent)	1.75%
Senior Secured Term Loan Facilities \| Maximum \| Subsequent Event \| Base Rate
Subsequent Event [Line Items]
Basis spread on debt instrument (as a percent)	0.75%