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Number of shares of the reporting entity held as investments by employees in the reporting entity's defined benefit plan.

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The percentage of an employee's investment that can be invested in the reporting entity's common stock.

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Percentage vest per year employed.

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Sharebased compensation arrangement by sharebased payment percentage of target restricted stock unit.

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The number of unissued shares under the reporting entity's previous stock plan that remain available to issue under the reporting entity's current stock plan.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of cost for defined contribution plan.

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Maximum amount the employee may contribute to a defined contribution plan.

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Name of defined contribution plan designed to provide retirement benefits. Includes, but is not limited to, legal name of plan.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The highest quantity of shares an employee can purchase under the plan per period.

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Employee Benefit Plans - Additional Information (Detail)				12 Months Ended
	Dec. 15, 2017 shares	Dec. 01, 2017 shares	May 19, 2017 USD ($) shares	Dec. 31, 2018 USD ($) Pension_Plan shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Defined benefit plan				$ 363,600,000	$ 286,500,000	$ 248,100,000
Plan name				CBRE 401(k) Plan
Defined Contribution Plan, Sponsor Location [Extensible List]				us-gaap:DomesticPlanMember
Company contribution percent per year employed				20.00%
Percent of annual compensation match percentage					50.00%	50.00%
Percent of annual compensation to be matched					6.00%	6.00%
Defined benefit plan, annual compensation expense maximum					$ 150,000	$ 150,000
Defined contribution plan, expenses recognized				$ 46,300,000	38,800,000	$ 44,300,000
Percent of 401(k) that can be invested in common stock				25.00%
Number of share held as investment under 401(k) Plan \| shares				1,300,000
Defined Benefit Plan, Type [Extensible List]				us-gaap:PensionPlansDefinedBenefitMember
Defined Benefit Plan, Sponsor Location [Extensible List]				us-gaap:ForeignPlanMember
Number of contributory defined benefit pension plans in the United Kingdom \| Pension_Plan				2
Fair value of plan assets				$ 274,400,000	333,500,000
Benefit obligation				387,400,000	455,600,000
Funded status				113,000,000	122,100,000
Unamortized actuarial loss				$ 192,700,000	$ 194,300,000
Annual Base Salary of Less than $100,000 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of annual compensation match percentage				67.00%
Percent of annual compensation to be matched				6.00%
Defined benefit plan, annual compensation expense maximum				$ 100,000
Annual Base Salary of $100,000 or Up to $150,000 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of annual compensation match percentage				50.00%
Percent of annual compensation to be matched				6.00%
Defined benefit plan, annual compensation expense minimum				$ 100,000,000
Defined benefit plan, annual compensation expense maximum				$ 150,000
Time Based Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
Time-vesting awards, portion to be vested per year				25.00%
Restricted Stock Units [Member] \| Time Based Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares				1,332,085	1,466,986	1,436,310
Restricted Stock Units [Member] \| Time Based Vesting [Member] \| Senior Brokers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Granted, Shares / Units \| shares	127,160
Restricted Stock Units [Member] \| Performance Based Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares				1,014,269	1,458,033	60,098
Non-Vested Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares / Units \| shares				2,023,266	5,152,082	1,496,408
Stock options, compensation expense				$ 128,200,000	$ 93,100,000	$ 63,500,000
Stock options, unrecognized estimated compensation cost				$ 197,300,000
Weighted average period of recognition				3 years 3 months 18 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee subscription rate				75.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee subscription rate				1.00%
2017 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unissued common stock available for issuance \| shares			0
Equity incentive plan termination date				Mar. 03, 2027
Maximum number of share to be granted per person \| shares			3,300,000
Maximum amount of share to be granted per person			$ 5,000,000
2017 Equity Incentive Plan [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares				3,632,717
2017 Equity Incentive Plan [Member] \| Restricted Stock Units [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of trading days required for purposes of measuring shareholder return based on average closing price of common stock immediately preceding grant date		60 days
2017 Equity Incentive Plan [Member] \| Restricted Stock Units [Member] \| Time Based Vesting [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sharebased compensation arrangement by sharebased payment percentage of target restricted stock unit		33.30%
2017 Equity Incentive Plan [Member] \| Restricted Stock Units [Member] \| Total Shareholder Return [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan termination date		Dec. 01, 2023
Sharebased compensation arrangement by sharebased payment percentage of target restricted stock unit		33.30%
Share-based compensation arrangement by share-based payment award, measurement period		6 years
2017 Equity Incentive Plan [Member] \| Restricted Stock Units [Member] \| EPS [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan termination date		Dec. 31, 2023
Sharebased compensation arrangement by sharebased payment percentage of target restricted stock unit		33.30%
Share-based compensation arrangement by share-based payment award, measurement period		6 years
2017 Equity Incentive Plan [Member] \| Maximum [Member] \| Employee Stock Options And Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of equity incentive and stock option plans			10 years
2017 Equity Incentive Plan [Member] \| Maximum [Member] \| Restricted Stock Units [Member] \| Time Based Vesting [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares		939,605		35,031
2017 Equity Incentive Plan [Member] \| Maximum [Member] \| Restricted Stock Units [Member] \| Performance Based Vesting [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares		3,288,618		122,610
2017 Equity Incentive Plan [Member] \| Minimum [Member] \| Time Based Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
2012 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant \| shares				3,255,964
Class A Common Stock [Member] \| 2017 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance \| shares			10,000,000