New Accounting Pronouncements - Schedule of Adoption of New Revenue Recognition Guidance on Financial Statement - Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 5,260,954	$ 4,638,596	$ 15,046,340	$ 13,129,133
Cost of services	4,098,904	3,598,279	11,677,613	10,154,296
Operating, administrative and other	859,085	704,950	2,417,602	2,024,191
Operating income	189,717	238,956	628,642	672,495
Income before provision for income taxes	386,652	277,204	882,891	742,844
Provision for income taxes	94,963	77,072	211,446	200,778
Net income	291,689	200,132	671,445	542,066
Net income attributable to CBRE Group, Inc.	$ 290,469	$ 199,088	$ 669,424	$ 537,885
Basic income per share attributable to CBRE Group, Inc. shareholders	$ 0.86	$ 0.59	$ 1.97	$ 1.59
Diluted income per share attributable to CBRE Group, Inc. shareholders	$ 0.85	$ 0.58	$ 1.95	$ 1.58
As Reported [Member] \| ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue		$ 3,549,977		$ 9,873,396
Cost of services		2,513,377		6,919,018
Operating, administrative and other		704,898		2,023,503
Operating income		235,291		652,724
Income before provision for income taxes		273,539		723,073
Provision for income taxes		76,178		195,813
Net income		197,361		527,260
Net income attributable to CBRE Group, Inc.		$ 196,317		$ 523,079
Basic income per share attributable to CBRE Group, Inc. shareholders		$ 0.58		$ 1.55
Diluted income per share attributable to CBRE Group, Inc. shareholders		$ 0.58		$ 1.54
Adoption of New Revenue Recognition Guidance [Member] \| ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue		$ 1,088,619		$ 3,255,737
Cost of services		1,084,902		3,235,278
Operating, administrative and other		52		688
Operating income		3,665		19,771
Income before provision for income taxes		3,665		19,771
Provision for income taxes		894		4,965
Net income		2,771		14,806
Net income attributable to CBRE Group, Inc.		$ 2,771		$ 14,806
Basic income per share attributable to CBRE Group, Inc. shareholders		$ 0.01		$ 0.04
Diluted income per share attributable to CBRE Group, Inc. shareholders				$ 0.04

New Accounting Pronouncements - Schedule of Adoption of New Revenue Recognition Guidance on Financial Statement - Consolidated Statements of Operations (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

9 Months Ended

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2018

Sep. 30, 2017

New Accounting Pronouncements Or Change In Accounting Principle [Line Items]

Revenue

$ 5,260,954

$ 4,638,596

$ 15,046,340

$ 13,129,133