Segment Reporting - Consolidated Revenues and Assets Based on Geographical Focus of Associated Investment Vehicle (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Geographic Reporting Disclosure [Line Items]
Revenues	$ 755.3	$ 858.5	$ 248.4	$ 1,110.9	$ 831.8	$ (59.6)	$ 755.8	$ 1,317.3	$ 2,973.1	$ 2,845.3	$ 2,798.9
Assets	31,566.6				24,651.7				31,566.6	24,651.7	17,062.8
Percentage of Revenues									100.00%	100.00%	100.00%
Percentage of Assets									100.00%	100.00%	100.00%
Americas [Member]
Geographic Reporting Disclosure [Line Items]
Revenues									1,842.6	2,416.6	1,724.2
Assets	16,419.7				12,784.4				16,419.7	12,784.4	11,551.6
Percentage of Revenues									62.00%	85.00%	62.00%
Percentage of Assets									52.00%	52.00%	68.00%
EMEA [Member]
Geographic Reporting Disclosure [Line Items]
Revenues									756.2	503.0	586.1
Assets	14,670.8				11,342.9				14,670.8	11,342.9	4,264.5
Percentage of Revenues									25.00%	18.00%	21.00%
Percentage of Assets									46.00%	46.00%	25.00%
Asia-pacific [Member]
Geographic Reporting Disclosure [Line Items]
Revenues									374.3	(74.3)	488.6
Assets	$ 476.1				$ 524.4				$ 476.1	$ 524.4	$ 1,246.7
Percentage of Revenues									13.00%	(3.00%)	17.00%
Percentage of Assets									2.00%	2.00%	7.00%