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BASIS OF PRESENTATION, CONSOLIDATION AND SUMMARY OF ACCOUNTING POLICIES - Goodwill and Intangible Franchise Rights (Details)	12 Months Ended
	Dec. 31, 2024 region
U.S and U.K
Segment Reporting Information
Number of geographic regions	2

X

- Definition

Number of geographic regions

+ References

No definition available.

+ Details

Name:	gpi_NumberOfGeographicRegions
Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_ReportingUnitAxis=gpi_UnitedStatesAndUnitedKingdomMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: