DEBT - Composition of Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2021	Oct. 21, 2021	Dec. 31, 2020
Debt Instrument
Finance leases	$ 172.7		$ 124.7
Total other debt	967.4		748.3
Total debt	2,046.7		1,346.1
Less: unamortized discount	11.0		9.5
Less: current maturities	220.4		56.0
Total long-term debt	1,815.3		1,280.6
Other Debt
Debt Instrument
Real estate related and other long-term debt	$ 166.9		15.7
4.00% Senior Notes
Debt Instrument
Interest rate (as a percentage)		4.00%
4.00% Senior Notes \| Senior Notes
Debt Instrument
Interest rate (as a percentage)	4.00%	4.00%
Senior notes	$ 750.0		550.0
Acquisition Line \| Line of credit
Debt Instrument
Acquisition Line	329.3		47.8
Real estate related \| Other Debt
Debt Instrument
Real estate related and other long-term debt	$ 627.7		$ 607.8

Long term debt and capital lease obligations excluding short term financing current.

No definition available.

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Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Long-Term Debt And Finance Lease, Liability

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

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-Publisher FASB
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- 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.

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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+ Details

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Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Balance Type:	credit
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- Definition

Amount of long-term debt and lease obligation, classified as noncurrent.

+ References

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- Definition

Amount of long-term debt classified as other.

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- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

+ Details

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- Details

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- Details

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- Details

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