Segment Reporting - Consolidated Revenues and Assets Based on Geographical Focus of Associated Investment Vehicle (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Share of Total Revenues	$ 1,007.8	$ 639.9	$ 908.4	$ 1,120.1	$ 575.9	$ 607.3	$ 608.0	$ 483.1	$ 3,676.2	$ 2,274.3	$ 3,006.2
Percentages Of Revenue By Geographic Regions									100.00%	100.00%	100.00%
Assets	12,280.6				9,973.0				$ 12,280.6	$ 9,973.0	$ 32,181.6
Percentage Of Assets By Geographic Regions									100.00%	100.00%	100.00%
Americas
Segment Reporting Information [Line Items]
Share of Total Revenues									$ 2,299.0	$ 1,473.5	$ 1,518.7
Percentages Of Revenue By Geographic Regions									62.00%	65.00%	51.00%
Assets	5,033.5				5,048.7				$ 5,033.5	$ 5,048.7	$ 19,049.3
Percentage Of Assets By Geographic Regions									41.00%	50.00%	59.00%
EMEA
Segment Reporting Information [Line Items]
Share of Total Revenues									$ 837.6	$ 615.1	$ 1,090.1
Percentages Of Revenue By Geographic Regions									23.00%	27.00%	36.00%
Assets	6,085.6				4,245.1				$ 6,085.6	$ 4,245.1	$ 12,369.1
Percentage Of Assets By Geographic Regions									50.00%	43.00%	39.00%
Asia-Pacific
Segment Reporting Information [Line Items]
Share of Total Revenues									$ 539.6	$ 185.7	$ 397.4
Percentages Of Revenue By Geographic Regions									15.00%	8.00%	13.00%
Assets	$ 1,161.5				$ 679.2				$ 1,161.5	$ 679.2	$ 763.2
Percentage Of Assets By Geographic Regions									9.00%	7.00%	2.00%