Goodwill and Other Intangible Assets - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Business Software	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 01, 2017 USD ($)	Oct. 01, 2016 USD ($)	Oct. 01, 2015 USD ($)
Finite-Lived Intangible Assets [Line Items]
Number of acquisitions completed during the period | Business	11
Number of software service acquired | Software	2
Goodwill impairment	$ 1,068,506,000	$ 1,068,506,000	$ 1,068,506,000	$ 0	$ 0	$ 0
Other intangible assets, net	1,399,112,000	1,411,039,000
Other intangible assets, accumulated amortization	1,000,738,000	771,673,000
Indefinite lived intangible assets excluding goodwill	163,553,000	176,255,000
Amortization expense	238,700,000	211,700,000	175,300,000
Estimated annual amortization expense, 2018	216,200,000
Estimated annual amortization expense, 2019	165,000,000
Estimated annual amortization expense, 2020	138,200,000
Estimated annual amortization expense, 2021	117,000,000
Estimated annual amortization expense, 2022	107,100,000
Mortgage servicing rights [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	$ 235,626,000	180,563,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	10 years
Management contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	$ 122,450,000	99,733,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	13 years
Indefinite lived intangible assets excluding goodwill	$ 90,503,000	101,355,000
Other amortizable intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	164,796,000	141,316,000
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets excluding goodwill	56,800,000	56,800,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	$ 355,642,000	270,447,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	20 years
Trade names [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets excluding goodwill	$ 16,250,000	18,100,000
Non-compete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	$ 57,358,000	$ 32,777,000
Global Workplace Solutions (GWS) [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net servicing income expected to received, Maximum, years	20 years
Amortization expense			$ 24,200,000
Global Workplace Solutions (GWS) [Member] | Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets excluding goodwill	$ 280,000,000
Global Workplace Solutions (GWS) [Member] | Non-compete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net servicing income expected to received, Maximum, years	3 years
Indefinite lived intangible assets excluding goodwill	$ 74,000,000
Interactive Visualization Technologies [Member]
Finite-Lived Intangible Assets [Line Items]
Number of software service acquired | Software	1
Technology Solutions [Member]
Finite-Lived Intangible Assets [Line Items]
Number of software service acquired | Software	1