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v3.20.4

Subsequent Events (Details) - USD ($) $ in Millions |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Feb. 03, 2021 | Dec. 31, 2020 | Feb. 04, 2021 | Jan. 31, 2021 | Dec. 31, 2015
Subsequent Event [Line Items] |  |  |  |  |
Share repurchase program, authorized amount |  |  |  |  | $ 1,200
Stock repurchase program, remaining authorized repurchase amount |  | $ 600 |  |  |
Restricted stock units | Performance Shares |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Performance share, actual yielded performance, percent |  | 50.00% |  |  |
Subsequent Event |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Stock repurchase program, additional authorized amount |  |  | $ 300 |  |
Stock repurchase program, remaining authorized repurchase amount |  |  |  | $ 568 |
Subsequent Event | Restricted stock units | Performance Shares |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Performance share, actual yielded performance, percent | 95.00% |  |  |  |

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- Definition Share-Based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Actual Performance Percentage + References No definition available. + Details
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Namespace Prefix: | it_
Data Type: | num:percentItemType
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Period Type: | duration

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- Definition Stock Repurchase Program, Additional Authorized Amount + References No definition available. + Details
Name: | it_StockRepurchaseProgramAdditionalAuthorizedAmount
Namespace Prefix: | it_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount remaining of a stock repurchase plan authorized. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- 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 No definition available. + Details
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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
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