Business Combinations - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Mar. 31, 2020	May 24, 2019	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Goodwill	$ 8,544.1		$ 8,509.4	$ 7,157.1
OppenheimerFunds
ASSETS
Cash and cash equivalents	360.0
Accounts receivable	133.1
Investments	178.4
Prepaid assets	24.8
Other assets	181.2
Property, equipment and software, net	104.1
Intangible assets	5,189.0
Goodwill	1,507.6
Total assets	7,678.2
LIABILITES
Accrued compensation and benefits	263.9
Accounts payable and accrued expenses	730.4
Deferred tax liabilities, net	1,088.0
Total liabilities	2,082.3
Total identifiable net assets	5,595.9
Summary of consideration
Cash consideration	35.0	$ 35.0
Total cash and stock consideration	5,595.9
Common Shares | OppenheimerFunds
Summary of consideration
Stock consideration	1,453.6
Preferred Shares | OppenheimerFunds
Summary of consideration
Stock consideration	4,010.5	$ 4,000.0
Other consideration | OppenheimerFunds
Summary of consideration
Stock consideration	$ 96.8