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Fiduciary Funds - Additional Information (Detail) - USD ($) $ in Billions | Dec. 31, 2017 | Dec. 31, 2016
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Uncategorized [Abstract] |  |
Client deposit held | $ 4.0 | $ 3.4

X
- Definition The amount of funds held by the company on behalf of clients as of the balance sheet date. Such funds are not included in the reporting entity's consolidated balance sheet as the reporting entity does not own or have any legal rights to use these funds. + References No definition available. + Details
Name: | cbg_FiduciaryFunds
Namespace Prefix: | cbg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Uncategorized [Abstract] + References No definition available. + Details
Name: | cbg_UncategorizedAbstract
Namespace Prefix: | cbg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration