Segment Reporting - Total Segments to Partnership Income Before Provision for Taxes Reconciliation (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
Operating Statistics [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
Expenses	660.2	704.9	448.9	477.2	422.2	218.4	345.8	360.7	2,291.2	1,347.1	1,073.8
Other income (loss)									1,758.0	(315.4)	(245.4)
Economic net income (loss)									2,439.9	1,182.8	1,479.7
Total assets	31,566.6				24,651.7				31,566.6	24,651.7	17,062.8
Total Reportable Segment [Member]
Operating Statistics [Line Items]
Revenues									2,043.9	2,149.3	2,385.8
Expenses									1,308.3	1,316.2	1,371.8
Economic net income (loss)									735.6	833.1	1,014.0
Total assets	4,806.6				4,294.9				4,806.6	4,294.9
Consolidated Funds [Member]
Operating Statistics [Line Items]
Revenues									903.5	714.0	452.6
Expenses									923.9	592.2	278.0
Other income (loss)									1,755.5	(330.6)	(251.5)
Economic net income (loss)									1,735.1	(208.8)	(76.9)
Total assets	26,834.6				20,460.3				26,834.6	20,460.3
Reconciling Items [Member]
Operating Statistics [Line Items]
Revenues									25.7	(18.0)	(39.5)
Expenses									59.0	(561.3)	(576.0)
Other income (loss)									2.5	15.2	6.1
Economic net income (loss)									(30.8)	558.5	542.6
Total assets	$ (74.6)				$ (103.5)				$ (74.6)	$ (103.5)