Debt Instrument, Issue Price, Percentage

No definition available.

Name:	it_DebtInstrumentIssuePricePercentage
Namespace Prefix:	it_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Additional Borrowing Capacity

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

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

- Definition

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

+ References

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+ Details

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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.

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+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- 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.

+ References

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+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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Period Type:	instant

- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	it_DebtInstrumentRedemptionOptionAxis=it_DebtInstrumentRedemptionOptionOneMember
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Balance Type:
Period Type:

- Details

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- Details

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- Details

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- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Period Type:

- Details

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Period Type:

- Details

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- Details

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- Details

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- Details

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Balance Type:
Period Type:

- Details

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Debt - Narrative (Details) - USD ($)					9 Months Ended
Debt - Narrative (Details) - USD ($)	Mar. 26, 2024	Jun. 18, 2021	Sep. 28, 2020	Jun. 22, 2020	Sep. 30, 2024	Mar. 25, 2024	Dec. 31, 2023
2029 Notes \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 600,000,000.0
Debt instrument, fixed interest rate					3.625%		3.625%
Debt instrument, issue price, percent		100.00%
2029 Notes \| Senior Notes \| Debt Instrument Redemption Option One
Debt Instrument [Line Items]
Percentage of principal amount redeemed		40.00%
2030 Notes \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount			$ 800,000,000.0
Debt instrument, fixed interest rate					3.75%		3.75%
Debt instrument, issue price, percent			100.00%
Percentage of principal amount redeemed			40.00%
2028 Notes \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 800,000,000.0
Debt instrument, fixed interest rate					4.50%		4.50%
Debt instrument, issue price, percent				100.00%
Percentage of principal amount redeemed				40.00%
2020 Credit Agreement \| Term Loan Facility
Debt Instrument [Line Items]
Aggregate principal amount						$ 400,000,000
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt
Debt Instrument [Line Items]
Aggregate principal amount	$ 1,000,000,000
Debt term	5 years
Line of credit facility, additional borrowing capacity	$ 750,000,000
Long-term line of credit	$ 274,400,000
Additional interest above base rate					1.35%
Debt instrument, fixed interest rate					5.25%
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt \| Variable Rate Component One
Debt Instrument [Line Items]
Additional interest above base rate					0.10%
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt \| Minimum
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.125%
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt \| Minimum \| Variable Rate Component Two
Debt Instrument [Line Items]
Additional interest above base rate	1.125%
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt \| Maximum
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.25%
Revolving credit facility \| 2024 Credit Agreement \| Unsecured Debt \| Maximum \| Variable Rate Component Two
Debt Instrument [Line Items]
Additional interest above base rate	1.75%
Revolving credit facility \| 2020 Credit Agreement \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 1,000,000,000
Letter of Credit \| 2024 Credit Agreement \| Unsecured Debt
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 75,000,000