Goodwill and Other Intangible Assets - Schedule of Changes in Goodwill by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill Gross, Beginning	$ 3,402,327	$ 3,358,980
Accumulated impairment losses	(1,068,506)	(1,068,506)
Goodwill, Net of impairment losses	2,333,821	2,290,474
Purchase accounting entries related to acquisitions	859,676	145,118
Foreign exchange movement	(107,500)	(101,771)
Goodwill Gross, Ending	4,154,503	3,402,327
Accumulated impairment losses	(1,068,506)	(1,068,506)
Goodwill, Net of impairment losses	3,085,997	2,333,821
Americas [Member]
Goodwill [Line Items]
Goodwill Gross, Beginning	1,828,135	1,717,637
Accumulated impairment losses	(798,290)	(798,290)
Goodwill, Net of impairment losses	1,029,845	919,347
Purchase accounting entries related to acquisitions	434,452	112,024
Foreign exchange movement	(2,511)	(1,526)
Goodwill Gross, Ending	2,260,076	1,828,135
Accumulated impairment losses	(798,290)	(798,290)
Goodwill, Net of impairment losses	1,461,786	1,029,845
EMEA [Member]
Goodwill [Line Items]
Goodwill Gross, Beginning	836,054	890,138
Accumulated impairment losses	(138,631)	(138,631)
Goodwill, Net of impairment losses	697,423	751,507
Purchase accounting entries related to acquisitions	408,491	8,108
Foreign exchange movement	(72,395)	(62,192)
Goodwill Gross, Ending	1,172,150	836,054
Accumulated impairment losses	(138,631)	(138,631)
Goodwill, Net of impairment losses	1,033,519	697,423
Asia Pacific [Member]
Goodwill [Line Items]
Goodwill Gross, Beginning	151,682	138,493
Goodwill, Net of impairment losses	151,682	138,493
Purchase accounting entries related to acquisitions	16,733	24,986
Foreign exchange movement	(12,540)	(11,797)
Goodwill Gross, Ending	155,875	151,682
Goodwill, Net of impairment losses	155,875	151,682
Global Investment Management [Member]
Goodwill [Line Items]
Goodwill Gross, Beginning	499,793	526,049
Accumulated impairment losses	(44,922)	(44,922)
Goodwill, Net of impairment losses	454,871	481,127
Foreign exchange movement	(20,054)	(26,256)
Goodwill Gross, Ending	479,739	499,793
Accumulated impairment losses	(44,922)	(44,922)
Goodwill, Net of impairment losses	434,817	454,871
Development Services [Member]
Goodwill [Line Items]
Goodwill Gross, Beginning	86,663	86,663
Accumulated impairment losses	(86,663)	(86,663)
Goodwill Gross, Ending	86,663	86,663
Accumulated impairment losses	$ (86,663)	$ (86,663)