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Revenue - Schedule of Accounts Receivable and Deferred Revenues (Detail) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 USD ($)
Deferred Revenue - Short Term |
Contract With Customer Asset And Liability [Line Items] |
Deferred Revenue, Beginning balance | $ 74,332
Net increase (decrease) during the period | 20,341
Deferred Revenue, Ending balance | 94,673
Deferred Revenue - Long Term |
Contract With Customer Asset And Liability [Line Items] |
Deferred Revenue, Beginning balance | 2,049
Net increase (decrease) during the period | (276)
Deferred Revenue, Ending balance | $ 1,773

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- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130532-203044 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130549-203045 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044 + Details
Name: | us-gaap_ContractWithCustomerLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Contract with customer asset and liability. + References No definition available. + Details
Name: | wtw_ContractWithCustomerAssetAndLiabilityLineItems
Namespace Prefix: | wtw_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Contract with customer liability period increase decrease. + References No definition available. + Details
Name: | wtw_ContractWithCustomerLiabilityPeriodIncreaseDecrease
Namespace Prefix: | wtw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_ContractWithCustomerDurationAxis=us-gaap_ShortTermContractWithCustomerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ContractWithCustomerDurationAxis=us-gaap_LongTermContractWithCustomerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |