Debt Instrument, Issue Price, Percentage

No definition available.

Name:	it_DebtInstrumentIssuePricePercentage
Namespace Prefix:	it_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

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

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+ 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

+ Details

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

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

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
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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-Publisher FASB
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+ Details

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

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	it_DebtInstrumentRedemptionOptionAxis=it_DebtInstrumentRedemptionOptionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=it_SeniorNotesDue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=it_A2020CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	it_VariableRateComponentsAxis=it_VariableRateComponentOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=it_FederalReserveBoardOfNewYorkRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=it_TermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
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Balance Type:
Period Type:

Debt - Narrative (Details) - USD ($)			3 Months Ended
Debt - Narrative (Details) - USD ($)	Jun. 18, 2021	Sep. 28, 2020	Mar. 31, 2022	Jun. 22, 2020
2029 Notes \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount	$ 600,000,000		$ 600,000,000
Debt instrument, fixed interest rate	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	$ 800,000,000
Debt instrument, fixed interest rate		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	$ 800,000,000
Debt instrument, fixed interest rate				4.50%
Debt instrument, issue price, percent				100.00%
Percentage of principal amount redeemed			40.00%
2020 Credit Agreement \| Variable Rate Component, One \| Federal Reserve Board of New York Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
2020 Credit Agreement \| Term Loan Facility
Debt Instrument [Line Items]
Aggregate principal amount		$ 400,000,000
2020 Credit Agreement \| Line of Credit \| Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,000,000,000