Fair Value Measurement - Partnership's Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value On Recurring Basis [Line Items]
Assets	$ 24,018.5	$ 26,044.7
Loans payable of Consolidated Funds	17,046.7	16,052.2
Derivative instruments of the CLOs	29.1	17.2
Contingent consideration	20.8	51.1
Loans payable of a consolidated real estate VIE	75.4	146.2
Interest rate swaps	0.9	3.2
Foreign Currency Forward Contracts Measured At Fair Value Recurring Basis	2.8
Total Liabilities	17,175.7	16,269.9
Equity securities
Fair Value On Recurring Basis [Line Items]
Assets	1,141.7	2,472.1
Bonds
Fair Value On Recurring Basis [Line Items]
Assets	1,180.9	1,235.8
Loans
Fair Value On Recurring Basis [Line Items]
Assets	15,686.7	15,084.9
Partnership and LLC interests
Fair Value On Recurring Basis [Line Items]
Assets	3,143.3	3,481.0
Hedge funds
Fair Value On Recurring Basis [Line Items]
Assets	2,841.2	3,753.5
Other
Fair Value On Recurring Basis [Line Items]
Assets	5.0	1.5
Investments of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	23,998.8	26,028.8
Trading securities
Fair Value On Recurring Basis [Line Items]
Assets	1.4	3.3
Foreign currency forward contracts
Fair Value On Recurring Basis [Line Items]
Assets	1.7
Restricted securities of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	16.6	12.6
Level I
Fair Value On Recurring Basis [Line Items]
Assets	262.5	350.8
Loans payable of Consolidated Funds	0.0	0.0
Derivative instruments of the CLOs	0.0	0.0
Contingent consideration	0.0	0.0
Loans payable of a consolidated real estate VIE	0.0	0.0
Interest rate swaps	0.0	0.0
Foreign Currency Forward Contracts Measured At Fair Value Recurring Basis	0.0
Total Liabilities	0.0	0.0
Level I | Equity securities
Fair Value On Recurring Basis [Line Items]
Assets	254.6	346.8
Level I | Bonds
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Loans
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Partnership and LLC interests
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Hedge funds
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Other
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Investments of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	254.6	346.8
Level I | Trading securities
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level I | Foreign currency forward contracts
Fair Value On Recurring Basis [Line Items]
Assets	0.0
Level I | Restricted securities of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	7.9	4.0
Level II
Fair Value On Recurring Basis [Line Items]
Assets	3,154.7	3,910.3
Loans payable of Consolidated Funds	0.0	0.0
Derivative instruments of the CLOs	0.0	0.0
Contingent consideration	0.0	0.0
Loans payable of a consolidated real estate VIE	0.0	0.0
Interest rate swaps	0.9	3.2
Foreign Currency Forward Contracts Measured At Fair Value Recurring Basis	2.8
Total Liabilities	3.7	3.2
Level II | Equity securities
Fair Value On Recurring Basis [Line Items]
Assets	311.8	156.8
Level II | Bonds
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level II | Loans
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level II | Partnership and LLC interests
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level II | Hedge funds
Fair Value On Recurring Basis [Line Items]
Assets	2,841.2	3,753.5
Level II | Other
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level II | Investments of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	3,153.0	3,910.3
Level II | Trading securities
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level II | Foreign currency forward contracts
Fair Value On Recurring Basis [Line Items]
Assets	1.7
Level II | Restricted securities of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level III
Fair Value On Recurring Basis [Line Items]
Assets	20,601.3	21,783.6
Loans payable of Consolidated Funds	17,046.7	16,052.2
Derivative instruments of the CLOs	29.1	17.2
Contingent consideration	20.8	51.1
Loans payable of a consolidated real estate VIE	75.4	146.2
Interest rate swaps	0.0	0.0
Foreign Currency Forward Contracts Measured At Fair Value Recurring Basis	0.0
Total Liabilities	17,172.0	16,266.7
Level III | Equity securities
Fair Value On Recurring Basis [Line Items]
Assets	575.3	1,968.5
Level III | Bonds
Fair Value On Recurring Basis [Line Items]
Assets	1,180.9	1,235.8
Level III | Loans
Fair Value On Recurring Basis [Line Items]
Assets	15,686.7	15,084.9
Level III | Partnership and LLC interests
Fair Value On Recurring Basis [Line Items]
Assets	3,143.3	3,481.0
Level III | Hedge funds
Fair Value On Recurring Basis [Line Items]
Assets	0.0	0.0
Level III | Other
Fair Value On Recurring Basis [Line Items]
Assets	5.0	1.5
Level III | Investments of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	20,591.2	21,771.7
Level III | Trading securities
Fair Value On Recurring Basis [Line Items]
Assets	1.4	3.3
Level III | Foreign currency forward contracts
Fair Value On Recurring Basis [Line Items]
Assets	0.0
Level III | Restricted securities of Consolidated Funds
Fair Value On Recurring Basis [Line Items]
Assets	$ 8.7	$ 8.6