Supplemental Financial Information - Financial Position (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Assets
Cash and cash equivalents	$ 2,399.0		$ 987.6	$ 938.4
Cash and cash equivalents held at Consolidated Funds	134.8		148.6	377.8
Restricted cash	6.9		2.0	0.4
Investments, including accrued performance allocations of $8,100.3 million and $4,968.6 million as of September 30, 2021 and December 31, 2020, respectively	10,678.5		7,380.9
Investments of Consolidated Funds	6,469.7		6,056.9
Due from affiliates and other receivables, net	293.4		272.5
Due from affiliates and other receivables of Consolidated Funds, net	173.7		89.1
Fixed assets, net	139.2		149.2
Lease right-of-use assets, net	364.4		361.1
Deposits and other	72.4		51.7
Intangible assets, net	36.9		48.7
Deferred tax assets	19.8		96.5
Total assets	20,788.7		15,644.8
Liabilities and equity
Debt obligations	2,370.7		1,970.9
Loans payable of Consolidated Funds	5,955.1		5,563.0
Accounts payable, accrued expenses and other liabilities	374.5		286.3
Accrued compensation and benefits	4,710.2		3,222.6
Due to affiliates	391.2		436.7
Deferred revenue	334.0		89.0
Deferred tax liabilities	433.4		57.8
Other liabilities of Consolidated Funds	619.5		556.1
Lease liabilities	542.4		513.5
Accrued giveback obligations	24.7		18.7
Total liabilities	15,755.7		12,714.6
Common stock	3.6		3.5
Additional paid-in-capital	2,671.7		2,546.2
Retained earnings	2,324.1		348.2
Accumulated other comprehensive income (loss)	(240.2)		(208.7)
Non-controlling interests in consolidated entities	273.8		241.0
Total equity	5,033.0	$ 4,622.0	2,930.2	2,430.2	$ 2,142.7	$ 2,969.6
Total liabilities and equity	20,788.7		15,644.8
Accrued performance allocations	8,100.3		4,968.6
Consolidated Operating Entities
Assets
Cash and cash equivalents	2,399.0			938.4
Cash and cash equivalents held at Consolidated Funds	134.8			377.8
Restricted cash	6.9			$ 0.4
Consolidated Entities and Consolidated Funds
Assets
Total assets	6,778.2
Consolidated Entities and Consolidated Funds | Consolidated Operating Entities
Assets
Cash and cash equivalents	2,399.0		987.6
Cash and cash equivalents held at Consolidated Funds	0.0		0.0
Restricted cash	6.9		2.0
Investments, including accrued performance allocations of $8,100.3 million and $4,968.6 million as of September 30, 2021 and December 31, 2020, respectively	10,852.5		7,551.7
Investments of Consolidated Funds	0.0		0.0
Due from affiliates and other receivables, net	299.6		278.9
Due from affiliates and other receivables of Consolidated Funds, net	0.0		0.0
Fixed assets, net	139.2		149.2
Lease right-of-use assets, net	364.4		361.1
Deposits and other	72.4		51.7
Intangible assets, net	36.9		48.7
Deferred tax assets	19.8		96.5
Total assets	14,190.7		9,527.4
Liabilities and equity
Debt obligations	2,370.7		1,970.9
Loans payable of Consolidated Funds	0.0		0.0
Accounts payable, accrued expenses and other liabilities	374.5		286.3
Accrued compensation and benefits	4,710.2		3,222.6
Due to affiliates	391.2		436.7
Deferred revenue	334.0		89.0
Deferred tax liabilities	433.4		57.8
Other liabilities of Consolidated Funds	0.0		0.0
Lease liabilities	542.4		513.5
Accrued giveback obligations	24.7		18.7
Total liabilities	9,181.1		6,595.5
Common stock	3.6		3.5
Additional paid-in-capital	2,671.7		2,546.2
Retained earnings	2,324.1		348.2
Accumulated other comprehensive income (loss)	(237.6)		(205.8)
Non-controlling interests in consolidated entities	247.8		239.8
Total equity	5,009.6		2,931.9
Total liabilities and equity	14,190.7		9,527.4
Consolidated Entities and Consolidated Funds | Consolidated Funds
Assets
Cash and cash equivalents	0.0		0.0
Cash and cash equivalents held at Consolidated Funds	134.8		148.6
Restricted cash	0.0		0.0
Investments, including accrued performance allocations of $8,100.3 million and $4,968.6 million as of September 30, 2021 and December 31, 2020, respectively	0.0		0.0
Investments of Consolidated Funds	6,469.7		6,056.9
Due from affiliates and other receivables, net	0.0		0.0
Due from affiliates and other receivables of Consolidated Funds, net	173.7		89.1
Fixed assets, net	0.0		0.0
Lease right-of-use assets, net	0.0		0.0
Deposits and other	0.0		0.0
Intangible assets, net	0.0		0.0
Deferred tax assets	0.0		0.0
Total assets	6,778.2		6,294.6
Liabilities and equity
Debt obligations	0.0		0.0
Loans payable of Consolidated Funds	5,955.1		5,563.0
Accounts payable, accrued expenses and other liabilities	0.0		0.0
Accrued compensation and benefits	0.0		0.0
Due to affiliates	0.1		0.0
Deferred revenue	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other liabilities of Consolidated Funds	619.5		556.1
Lease liabilities	0.0		0.0
Accrued giveback obligations	0.0		0.0
Total liabilities	6,574.7		6,119.1
Common stock	0.0		0.0
Additional paid-in-capital	179.6		167.6
Retained earnings	0.0		0.0
Accumulated other comprehensive income (loss)	(2.1)		6.7
Non-controlling interests in consolidated entities	26.0		1.2
Total equity	203.5		175.5
Total liabilities and equity	6,778.2		6,294.6
Eliminations
Assets
Cash and cash equivalents	0.0		0.0
Cash and cash equivalents held at Consolidated Funds	0.0		0.0
Restricted cash	0.0		0.0
Investments, including accrued performance allocations of $8,100.3 million and $4,968.6 million as of September 30, 2021 and December 31, 2020, respectively	(174.0)		(170.8)
Investments of Consolidated Funds	0.0		0.0
Due from affiliates and other receivables, net	(6.2)		(6.4)
Due from affiliates and other receivables of Consolidated Funds, net	0.0		0.0
Fixed assets, net	0.0		0.0
Lease right-of-use assets, net	0.0		0.0
Deposits and other	0.0		0.0
Intangible assets, net	0.0		0.0
Deferred tax assets	0.0		0.0
Total assets	(180.2)		(177.2)
Liabilities and equity
Debt obligations	0.0		0.0
Loans payable of Consolidated Funds	0.0		0.0
Accounts payable, accrued expenses and other liabilities	0.0		0.0
Accrued compensation and benefits	0.0		0.0
Due to affiliates	(0.1)		0.0
Deferred revenue	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other liabilities of Consolidated Funds	0.0		0.0
Lease liabilities	0.0		0.0
Accrued giveback obligations	0.0		0.0
Total liabilities	(0.1)		0.0
Common stock	0.0		0.0
Additional paid-in-capital	(179.6)		(167.6)
Retained earnings	0.0		0.0
Accumulated other comprehensive income (loss)	(0.5)		(9.6)
Non-controlling interests in consolidated entities	0.0		0.0
Total equity	(180.1)		(177.2)
Total liabilities and equity	$ (180.2)		$ (177.2)