Supplemental Financial Information - Financial Position (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets
Cash and cash equivalents	$ 880.4	$ 987.6	$ 1,007.9
Cash and cash equivalents held at Consolidated Funds	174.6	148.6	170.9
Restricted cash	6.6	2.0	0.6
Investments, including accrued performance allocations of $6,532.0 million and $4,968.6 million as of March 31, 2021 and December 31, 2020, respectively	9,044.5	7,380.9
Investments of Consolidated Funds	5,824.8	6,056.9
Due from affiliates and other receivables, net	245.7	272.5
Due from affiliates and other receivables of Consolidated Funds, net	169.8	89.1
Fixed assets, net	148.9	149.2
Lease right-of-use assets, net	364.7	361.1
Deposits and other	51.8	51.7
Intangible assets, net	45.0	48.7
Deferred tax assets	18.5	96.5
Total assets	16,975.3	15,644.8
Liabilities and equity
Debt obligations	1,940.6	1,970.9
Loans payable of Consolidated Funds	5,459.8	5,563.0
Accounts payable, accrued expenses and other liabilities	215.5	286.3
Accrued compensation and benefits	3,579.3	3,222.6
Due to affiliates	408.1	436.7
Deferred revenue	343.8	89.0
Deferred tax liabilities	245.2	57.8
Other liabilities of Consolidated Funds	530.6	556.1
Lease liabilities	519.6	513.5
Accrued giveback obligations	20.6	18.7
Total liabilities	13,263.1	12,714.6
Common stock	3.5	3.5
Additional paid-in-capital	2,573.7	2,546.2
Retained earnings	1,118.8	348.2
Accumulated other comprehensive loss	(234.0)	(208.7)
Non-controlling interests in consolidated entities	250.2	241.0
Total equity	3,712.2	2,930.2	2,069.1	$ 2,969.6
Total liabilities and equity	16,975.3	15,644.8
Accrued performance allocations	6,532.0	4,968.6
Consolidated Operating Entities
Assets
Cash and cash equivalents	880.4		1,007.9
Cash and cash equivalents held at Consolidated Funds	174.6		170.9
Restricted cash	6.6		$ 0.6
Consolidated Entities and Consolidated Funds
Assets
Total assets	6,169.2
Consolidated Entities and Consolidated Funds | Consolidated Operating Entities
Assets
Cash and cash equivalents	880.4	987.6
Cash and cash equivalents held at Consolidated Funds	0.0	0.0
Restricted cash	6.6	2.0
Investments, including accrued performance allocations of $6,532.0 million and $4,968.6 million as of March 31, 2021 and December 31, 2020, respectively	9,219.1	7,551.7
Investments of Consolidated Funds	0.0	0.0
Due from affiliates and other receivables, net	251.5	278.9
Due from affiliates and other receivables of Consolidated Funds, net	0.0	0.0
Fixed assets, net	148.9	149.2
Lease right-of-use assets, net	364.7	361.1
Deposits and other	51.8	51.7
Intangible assets, net	45.0	48.7
Deferred tax assets	18.5	96.5
Total assets	10,986.5	9,527.4
Liabilities and equity
Debt obligations	1,940.6	1,970.9
Loans payable of Consolidated Funds	0.0	0.0
Accounts payable, accrued expenses and other liabilities	215.5	286.3
Accrued compensation and benefits	3,579.3	3,222.6
Due to affiliates	408.1	436.7
Deferred revenue	343.8	89.0
Deferred tax liabilities	245.2	57.8
Other liabilities of Consolidated Funds	0.0	0.0
Lease liabilities	519.6	513.5
Accrued giveback obligations	20.6	18.7
Total liabilities	7,272.7	6,595.5
Common stock	3.5	3.5
Additional paid-in-capital	2,573.7	2,546.2
Retained earnings	1,118.8	348.2
Accumulated other comprehensive loss	(231.3)	(205.8)
Non-controlling interests in consolidated entities	249.1	239.8
Total equity	3,713.8	2,931.9
Total liabilities and equity	10,986.5	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	174.6	148.6
Restricted cash	0.0	0.0
Investments, including accrued performance allocations of $6,532.0 million and $4,968.6 million as of March 31, 2021 and December 31, 2020, respectively	0.0	0.0
Investments of Consolidated Funds	5,824.8	6,056.9
Due from affiliates and other receivables, net	0.0	0.0
Due from affiliates and other receivables of Consolidated Funds, net	169.8	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	6,169.2	6,294.6
Liabilities and equity
Debt obligations	0.0	0.0
Loans payable of Consolidated Funds	5,459.8	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	0.0	0.0
Deferred revenue	0.0	0.0
Deferred tax liabilities	0.0	0.0
Other liabilities of Consolidated Funds	530.6	556.1
Lease liabilities	0.0	0.0
Accrued giveback obligations	0.0	0.0
Total liabilities	5,990.4	6,119.1
Common stock	0.0	0.0
Additional paid-in-capital	177.4	167.6
Retained earnings	0.0	0.0
Accumulated other comprehensive loss	0.3	6.7
Non-controlling interests in consolidated entities	1.1	1.2
Total equity	178.8	175.5
Total liabilities and equity	6,169.2	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 $6,532.0 million and $4,968.6 million as of March 31, 2021 and December 31, 2020, respectively	(174.6)	(170.8)
Investments of Consolidated Funds	0.0	0.0
Due from affiliates and other receivables, net	(5.8)	(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	(180.4)	(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	0.0	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	0.0	0.0
Common stock	0.0	0.0
Additional paid-in-capital	(177.4)	(167.6)
Retained earnings	0.0	0.0
Accumulated other comprehensive loss	(3.0)	(9.6)
Non-controlling interests in consolidated entities	0.0	0.0
Total equity	(180.4)	(177.2)
Total liabilities and equity	$ (180.4)	$ (177.2)