Guarantor and Nonguarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 710,505	$ 450,315	$ 651,897
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(178,042)	(191,205)	(139,464)
Acquisition of businesses (other than GWS), including net assets acquired, intangibles and goodwill, net of cash acquired	(142,433)	(31,634)	(161,106)
Contributions to unconsolidated subsidiaries	(68,700)	(66,816)	(71,208)
Distributions from unconsolidated subsidiaries	247,574	213,446	187,577
Decrease (increase) in restricted cash	1,281	(2,552)	(49,012)
Purchase of available for sale securities	(34,864)	(37,661)	(40,287)
Proceeds from the sale of available for sale securities	31,377	35,051	42,572
Other investing activities, net	2,392	40,083	30,048
Net cash used in investing activities	(141,415)	(7,439)	(1,618,959)
Acquisition of GWS, including net assets acquired, intangibles and goodwill		(10,477)	(1,421,663)
Net proceeds from disposition of real estate held for investment		44,326	3,584
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from senior term loans	200,000		900,000
Repayment of senior term loans	(751,876)	(136,250)	(657,488)
Proceeds from revolving credit facility	1,521,000	2,909,000	2,643,500
Repayment of revolving credit facility	(1,521,000)	(2,909,000)	(2,648,012)
Proceeds from notes payable on real estate held for investment	137	7,274
Proceeds from issuance of senior notes, net			595,440
Repayment of notes payable on real estate held for investment	(1,779)	(33,944)	(1,576)
Proceeds from notes payable on real estate held for sale and under development	4,196	17,727	20,879
Repayment of notes payable on real estate held for sale and under development	(10,777)	(4,102)	(1,186)
Shares and units repurchased for payment of taxes on equity awards	(29,549)	(27,426)	(24,523)
Non-controlling interest contributions	5,301	2,272	5,909
Non-controlling interest distributions	(8,715)	(19,133)	(16,582)
Payment of financing costs	(7,999)	(5,618)	(30,664)
Other financing activities, net	(2,675)	(443)	3,851
Net cash (used in) provided by financing activities	(603,736)	(199,643)	789,548
Effect of currency exchange rate changes on cash and cash equivalents	23,844	(21,060)	(22,967)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(10,802)	222,173	(200,481)
CASH AND CASH EQUIVALENTS, AT BEGINNING OF PERIOD	762,576	540,403	740,884
CASH AND CASH EQUIVALENTS, AT END OF PERIOD	751,774	762,576	540,403
Cash paid during the period for:
Interest	117,164	125,800	88,078
Income taxes, net	356,997	294,848	285,730
Parent [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	89,341	84,393	33,959
CASH FLOWS FROM FINANCING ACTIVITIES:
Shares and units repurchased for payment of taxes on equity awards	(29,549)	(27,426)	(24,523)
(Increase) decrease in intercompany receivables, net	(60,271)	(57,880)	(19,238)
Other financing activities, net	479	915	9,802
Net cash (used in) provided by financing activities	(89,341)	(84,391)	(33,959)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS		2
CASH AND CASH EQUIVALENTS, AT BEGINNING OF PERIOD	7	5	5
CASH AND CASH EQUIVALENTS, AT END OF PERIOD	7	7	5
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	241,015	212,841	452,304
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(121,347)	(115,049)	(84,933)
Acquisition of businesses (other than GWS), including net assets acquired, intangibles and goodwill, net of cash acquired	(107,102)	(6,572)	(153,690)
Contributions to unconsolidated subsidiaries	(63,119)	(47,192)	(66,966)
Distributions from unconsolidated subsidiaries	236,806	206,011	179,699
Decrease (increase) in restricted cash	4,872	(546)	(5,791)
Purchase of available for sale securities	(34,864)	(37,661)	(40,287)
Proceeds from the sale of available for sale securities	31,377	35,051	42,572
Other investing activities, net	1,968	19,178	16,172
Net cash used in investing activities	(51,409)	56,476	(842,953)
Acquisition of GWS, including net assets acquired, intangibles and goodwill		3,256	(729,729)
CASH FLOWS FROM FINANCING ACTIVITIES:
(Increase) decrease in intercompany receivables, net	(338,534)	(151,433)	167,505
Other financing activities, net	(3,145)	(1,173)	(3,549)
Net cash (used in) provided by financing activities	(341,679)	(152,606)	163,956
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(152,073)	116,711	(226,693)
CASH AND CASH EQUIVALENTS, AT BEGINNING OF PERIOD	264,121	147,410	374,103
CASH AND CASH EQUIVALENTS, AT END OF PERIOD	112,048	264,121	147,410
Cash paid during the period for:
Interest			126
Income taxes, net	198,520	174,164	179,418
Nonguarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	342,159	176,724	173,111
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(56,695)	(76,156)	(54,531)
Acquisition of businesses (other than GWS), including net assets acquired, intangibles and goodwill, net of cash acquired	(35,331)	(25,062)	(7,416)
Contributions to unconsolidated subsidiaries	(5,581)	(19,624)	(4,242)
Distributions from unconsolidated subsidiaries	10,768	7,435	7,878
Decrease (increase) in restricted cash	(3,591)	(2,006)	(43,221)
Other investing activities, net	424	20,905	13,876
Net cash used in investing activities	(90,006)	(63,915)	(776,006)
Acquisition of GWS, including net assets acquired, intangibles and goodwill		(13,733)	(691,934)
Net proceeds from disposition of real estate held for investment		44,326	3,584
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of revolving credit facility			(4,512)
Proceeds from notes payable on real estate held for investment	137	7,274
Repayment of notes payable on real estate held for investment	(1,779)	(33,944)	(1,576)
Proceeds from notes payable on real estate held for sale and under development	4,196	17,727	20,879
Repayment of notes payable on real estate held for sale and under development	(10,777)	(4,102)	(1,186)
Non-controlling interest contributions	5,301	2,272	5,909
Non-controlling interest distributions	(8,715)	(19,133)	(16,582)
Payment of financing costs	(21)	(159)	(85)
(Increase) decrease in intercompany receivables, net	(121,774)	35,551	661,412
Other financing activities, net	(9)	(185)	(2,402)
Net cash (used in) provided by financing activities	(133,441)	5,301	661,857
Effect of currency exchange rate changes on cash and cash equivalents	23,844	(21,060)	(22,967)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	142,556	97,050	35,995
CASH AND CASH EQUIVALENTS, AT BEGINNING OF PERIOD	481,559	384,509	348,514
CASH AND CASH EQUIVALENTS, AT END OF PERIOD	624,115	481,559	384,509
Cash paid during the period for:
Interest	92	3,195	1,390
Income taxes, net	158,477	120,684	106,312
CBRE Services [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	37,990	(23,643)	(7,477)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from senior term loans	200,000		900,000
Repayment of senior term loans	(751,876)	(136,250)	(657,488)
Proceeds from revolving credit facility	1,521,000	2,909,000	2,643,500
Repayment of revolving credit facility	(1,521,000)	(2,909,000)	(2,643,500)
Proceeds from issuance of senior notes, net			595,440
Payment of financing costs	(7,978)	(5,459)	(30,579)
(Increase) decrease in intercompany receivables, net	520,579	173,762	(809,679)
Net cash (used in) provided by financing activities	(39,275)	32,053	(2,306)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(1,285)	8,410	(9,783)
CASH AND CASH EQUIVALENTS, AT BEGINNING OF PERIOD	16,889	8,479	18,262
CASH AND CASH EQUIVALENTS, AT END OF PERIOD	15,604	16,889	8,479
Cash paid during the period for:
Interest	$ 117,072	$ 122,605	$ 86,562

Cash paid during period for.

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The cash inflow from notes payable borrowings associated with real estate held for investment.

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The cash inflow from notes payable borrowings associated with real estate held for sale and real estate under development.

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The cash outflow resulting from the repayment of notes payable associated with real estate held for investment.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

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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.

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Amount of increase (decrease) from the effect of exchange rate changes on cash and cash equivalent balances held in foreign currencies.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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The net cash inflow or outflow for the increase (decrease) associated with funds that are not available for withdrawal or use (such as funds held in escrow) and are associated with underlying transactions that are classified as investing activities.

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Amount of cash paid for interest. Includes, but is not limited to, payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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Amount of cash inflow (outflow) of financing activities, excluding discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) of investing activities, excluding discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, excluding discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cash outflow for loan and debt issuance costs.

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Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity.

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The cash outflow associated with a second acquisition of a business, net of the cash acquired from the purchase.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest.

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of cash inflow from a noncontrolling interest. Includes, but is not limited to, purchase of additional shares or other increase in noncontrolling interest ownership.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Paragraph 14
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Amount of cash inflow (outflow) from financing activities classified as other.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of cash inflow (outflow) from long-term debt by a related party. Related parties, include, but are not limited to, affiliates, owners or officers and their immediate families, and pension trusts.

+ References

No definition available.

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Amount of cash inflow (outflow) from long-term debt wholly or partially secured by collateral. Excludes tax exempt secured debt.

+ References

No definition available.

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
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-Paragraph 15
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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