Fair Value Measurement - Partnership's Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets
Subtotal	$ 7,962.9	$ 7,577.8
Liabilities
Loans payable of Consolidated Funds	6,298.6	5,491.6
Total Liabilities	6,298.6	5,494.8
Senior and Subordinated Notes
Liabilities
Loans payable of Consolidated Funds	10.0
Senior secured notes
Liabilities
Loans payable of Consolidated Funds		235.6
Revolving Credit Facililty
Liabilities
Loans payable of Consolidated Funds	177.9	178.0
Equity securities | Variable Interest Entity, Primary Beneficiary
Assets
Investments measured at net asset value	322.0	377.4
Foreign currency forward contracts
Liabilities
Foreign currency forward contracts		3.2
Fair Value, Inputs, Level 1, 2 and 3
Assets
Subtotal	7,460.9	7,049.3
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities
Assets
Investments of consolidated funds	377.6	430.6
Fair Value, Inputs, Level 1, 2 and 3 | Bonds
Assets
Investments of consolidated funds	522.5	594.9
Fair Value, Inputs, Level 1, 2 and 3 | Loans
Assets
Investments of consolidated funds	5,862.1	5,352.9
Fair Value, Inputs, Level 1, 2 and 3 | Investments of Consolidated Funds
Assets
Investments of consolidated funds	6,762.2	6,378.4
Fair Value, Inputs, Level 1, 2 and 3 | Investments in CLOs
Assets
Investments of consolidated funds	532.6	526.1
Fair Value, Inputs, Level 1, 2 and 3 | Other investments
Assets
Investments of consolidated funds	166.1	122.6
Fair Value, Inputs, Level 1, 2 and 3 | Investments in CLOs and other, and Partnership and LLC interests
Assets
Investments of consolidated funds	698.7	648.7
Fair Value, Inputs, Level 1, 2 and 3 | Corporate treasury investments:
Assets
Subtotal		20.0
Fair Value, Inputs, Level 1, 2 and 3 | Commercial paper and other
Assets
Subtotal		20.0
Fair Value, Inputs, Level 1, 2 and 3 | Foreign currency forward contracts
Assets
Foreign currency forward contracts		2.2
Level I
Assets
Subtotal	38.7	1.6
Liabilities
Loans payable of Consolidated Funds	0.0	0.0
Total Liabilities	0.0	0.0
Level I | Equity securities
Assets
Investments of consolidated funds	0.0	0.0
Level I | Bonds
Assets
Investments of consolidated funds	0.0	0.0
Level I | Loans
Assets
Investments of consolidated funds	0.0	0.0
Level I | Investments of Consolidated Funds
Assets
Investments of consolidated funds	0.0	0.0
Level I | Investments in CLOs
Assets
Investments of consolidated funds	0.0	0.0
Level I | Other investments
Assets
Investments of consolidated funds	38.7	1.6
Level I | Investments in CLOs and other, and Partnership and LLC interests
Assets
Investments of consolidated funds	38.7	1.6
Level I | Corporate treasury investments:
Assets
Subtotal		0.0
Level I | Commercial paper and other
Assets
Subtotal		0.0
Level I | Foreign currency forward contracts
Assets
Foreign currency forward contracts		0.0
Liabilities
Foreign currency forward contracts		0.0
Level II
Assets
Subtotal	42.8	63.8
Liabilities
Loans payable of Consolidated Funds	0.0	0.0
Total Liabilities	0.0	3.2
Level II | Equity securities
Assets
Investments of consolidated funds	0.0	0.0
Level II | Bonds
Assets
Investments of consolidated funds	0.0	0.0
Level II | Loans
Assets
Investments of consolidated funds	0.0	0.0
Level II | Investments of Consolidated Funds
Assets
Investments of consolidated funds	0.0	0.0
Level II | Investments in CLOs
Assets
Investments of consolidated funds	0.0	0.0
Level II | Other investments
Assets
Investments of consolidated funds	42.8	41.6
Level II | Investments in CLOs and other, and Partnership and LLC interests
Assets
Investments of consolidated funds	42.8	41.6
Level II | Corporate treasury investments:
Assets
Subtotal		20.0
Level II | Commercial paper and other
Assets
Subtotal		20.0
Level II | Foreign currency forward contracts
Assets
Foreign currency forward contracts		2.2
Liabilities
Foreign currency forward contracts		3.2
Level III
Assets
Subtotal	7,379.4	6,983.9
Liabilities
Loans payable of Consolidated Funds	6,298.6	5,491.6
Total Liabilities	6,298.6	5,491.6
Level III | Equity securities
Assets
Investments of consolidated funds	377.6	430.6
Investments measured at net asset value	50.4	58.2
Level III | Bonds
Assets
Investments of consolidated funds	522.5	594.9
Subtotal		594.9
Level III | Loans
Assets
Investments of consolidated funds	5,862.1	5,352.9
Subtotal		5,043.4
Level III | Investments of Consolidated Funds
Assets
Investments of consolidated funds	6,762.2	6,378.4
Subtotal	6,762.2	6,378.4
Level III | Investments in CLOs
Assets
Investments of consolidated funds	532.6	526.1
Level III | Other investments
Assets
Investments of consolidated funds	84.6	79.4
Level III | Investments in CLOs and other, and Partnership and LLC interests
Assets
Investments of consolidated funds	617.2	605.5
Level III | Corporate treasury investments:
Assets
Subtotal		0.0
Level III | Commercial paper and other
Assets
Subtotal		0.0
Level III | Foreign currency forward contracts
Assets
Foreign currency forward contracts		0.0
Liabilities
Foreign currency forward contracts		0.0
Fair Value Measured at NAV
Assets
Subtotal	502.0
Investments measured at net asset value		$ 528.5
Fair Value Measured at NAV | Investments of Consolidated Funds
Assets
Investments of consolidated funds	$ 490.9