Ratio of EBITDA as defined in the Credit Agreement to interest expense calculated over a trailing twelve month period.

No definition available.

Name:	cbg_CoverageRatioOfEarningsBeforeInterestTaxDepreciationAndAmortizationToInterestExpense
Namespace Prefix:	cbg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Leverage ratio of total debt to EBITDA.

+ References

No definition available.

+ Details

Name:	cbg_LeverageRatioOfDebtToEarningsBeforeInterestTaxDepreciationAndAmortization
Namespace Prefix:	cbg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Reflects when the latest date in which the reporting entity's credit facilities terminate, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

No definition available.

+ Details

Name:	cbg_LineOfCreditFacilityLatestExpirationDate
Namespace Prefix:	cbg_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the maximum ratio of debt less available cash to earnings before interest, taxes, depreciation and amortization (EBITDA) allowed in the reporting entity's credit agreement.

+ References

No definition available.

+ Details

Name:	cbg_MaximumLeverageRatioOfDebtToEarningsBeforeInterestTaxDepreciationAndAmortization
Namespace Prefix:	cbg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the minimum ratio of earnings before interest, taxes, depreciation and amortization (EBITDA) to total interest expense required in the reporting entity's credit agreement.

+ References

No definition available.

+ Details

Name:	cbg_MinimumCoverageRatioOfEarningsBeforeInterestTaxDepreciationAndAmortizationToInterestExpense
Namespace Prefix:	cbg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num: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

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=cbg_TwoThousandFifteenCreditAgreementMember
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:	us-gaap_CreditFacilityAxis=cbg_TrancheATermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

Long-Term Debt and Short-Term Borrowings - Credit Agreement - Additional Information (Detail)		6 Months Ended
	Mar. 21, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015
Debt Instrument [Line Items]
Credit facility expiration date		2017-06
Minimum coverage ratio of EBITDA to total interest expense		2.00
Maximum leverage ratio of total debt less available cash to EBITDA		4.25
Coverage ratio of EBITDA to total interest expense		12.15
Leverage ratio of total debt less available cash to EBITDA		1.61
5.00% Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate of long-term debt		5.00%	5.00%
5.25% Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate of long-term debt		5.25%	5.25%
4.875% Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate of long-term debt		4.875%	4.875%
2015 Credit Agreement [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 2,800,000,000
Revolving credit facility maturity date		Mar. 21, 2021
2015 Credit Agreement [Member] \| Revolving credit facility [Member]
Debt Instrument [Line Items]
Revolving credit facility increase in borrowing capacity	$ 200,000,000
Credit facility expiration date	2021-03
2015 Credit Agreement [Member] \| Tranche A term loan facility [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 500,000,000
Revolving credit facility maturity date		Jan. 09, 2020
2015 Credit Agreement [Member] \| Tranche B-1 term loan facility [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 270,000,000
Revolving credit facility maturity date		Sep. 03, 2020
2015 Credit Agreement [Member] \| Tranche B-2 term loan facility [Member]
Debt Instrument [Line Items]
Amounts available to borrow under Credit Agreement		$ 130,000,000
Revolving credit facility maturity date		Sep. 03, 2022