Long-Term Debt and Short-Term Borrowings - Revolving Credit Facility - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Revolving credit facility	$ 230,000,000
Letters of credit outstanding amount	78,300,000
2019 Credit Agreement [Member] \| Revolving credit facility [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement	2,800,000,000
Revolving credit facility	230,000,000.0
Letters of credit outstanding amount	$ 2,000,000.0
2019 Credit Agreement [Member] \| Revolving credit facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Credit Agreement applicable fixed rate spread	0.68%
Credit Agreement applicable daily rate spread	0.00%
2019 Credit Agreement [Member] \| Revolving credit facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Credit Agreement applicable fixed rate spread	1.075%
Credit Agreement applicable daily rate spread	0.075%
2019 Credit Agreement [Member] \| Canadian, Australian and New Zealand subsidiaries [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement	$ 200,000,000.0
2019 Credit Agreement [Member] \| U.K. subsidiaries [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement	300,000,000.0
2017 Credit Agreement [Member] \| Revolving credit facility [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement	$ 2,800,000,000
Revolving credit facility		$ 0
Letters of credit outstanding amount		$ 2,000,000.0
2017 Credit Agreement [Member] \| Revolving credit facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Credit Agreement applicable fixed rate spread		0.775%
Credit Agreement applicable daily rate spread		0.00%
2017 Credit Agreement [Member] \| Revolving credit facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Credit Agreement applicable fixed rate spread		1.075%
Credit Agreement applicable daily rate spread		0.075%
2017 Credit Agreement [Member] \| Canadian, Australian and New Zealand subsidiaries [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 200,000,000.0
2017 Credit Agreement [Member] \| U.K. subsidiaries [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 300,000,000.0

Long term debt percentage spread over daily interest rate.

No definition available.

Name:	cbre_LongTermDebtPercentageSpreadOverDailyInterestRate
Namespace Prefix:	cbre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Long term debt percentage spread over fixed interest rate.

+ References

No definition available.

+ Details

Name:	cbre_LongTermDebtPercentageSpreadOverFixedInterestRate
Namespace Prefix:	cbre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current portion 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=cbre_CanadianAustralianAndNewZealandSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=cbre_UnitedKingdomSubsidiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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