Segment Reporting - Total Segments to Partnership Income Before Provision for Taxes Reconciliation (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 575.9	$ 607.3	$ 608.0	$ 483.1	$ 715.8	$ 297.5	$ 856.1	$ 1,136.8	$ 2,274.3	$ 3,006.2	$ 3,880.3
Expenses	574.0	661.8	546.9	459.4	802.5	795.3	843.6	1,027.0	2,242.1	3,468.4	3,775.4
Other income	10.0	$ 4.8	$ 6.7	$ (8.4)	(71.4)	$ (31.3)	$ 461.6	$ 505.5	13.1	864.4	887.0
Economic net income									45.3	402.2	991.9
Total assets	9,973.0				32,181.6				9,973.0	32,181.6	35,994.3
Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues									1,958.6	2,132.4	3,022.0
Expenses									1,652.7	1,735.8	2,059.6
Other income									0.0	0.0	0.0
Economic net income									305.9	396.6	962.4
Total assets	5,457.3				6,104.6				5,457.3	6,104.6
Consolidated Funds
Segment Reporting Information [Line Items]
Revenues									166.9	975.5	956.0
Expenses									153.1	1,258.8	1,286.5
Other income									13.1	886.9	898.4
Economic net income									26.9	603.6	567.9
Total assets	4,684.7				26,395.7				4,684.7	26,395.7
Reconciling Items
Segment Reporting Information [Line Items]
Revenues									148.8	(101.7)	(97.7)
Expenses									436.3	473.8	429.3
Other income									0.0	(22.5)	(11.4)
Economic net income									(287.5)	(598.0)	$ (538.4)
Total assets	$ (169.0)				$ (318.7)				$ (169.0)	$ (318.7)