Segments - Adjusted EBITDA Calculation by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Net income attributable to CBRE Group, Inc.	$ 1,063,219	$ 697,109	$ 573,079
Depreciation and amortization	451,988	406,114	366,927
Interest expense	107,270	136,814	144,851
Write-off of financing costs on extinguished debt	27,982
Provision for income taxes	313,058	467,757	296,900
Interest income	8,585	9,853	8,051
EBITDA	1,954,932	1,697,941	1,373,706
Costs associated with our reorganization, including cost-savings initiatives	37,925
Integration and other costs related to acquisitions	9,124	27,351	125,743
Costs incurred in connection with litigation settlement	8,868
Carried interest incentive compensation reversal to align with the timing of associated revenue	(5,261)	(8,518)	(15,558)
One-time gain associated with remeasuring an investment in an unconsolidated subsidiary to fair value as of the date the remaining controlling interest was acquired	(100,420)
Cost-elimination expenses			78,456
Adjusted EBITDA	$ 1,905,168	$ 1,716,774	$ 1,562,347