Business Combinations (Assets Acquired and liabilities Assumed) (Details) - USD ($) $ in Millions	12 Months Ended	19 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
$ in millions
Goodwill	$ 8,916.3	$ 8,916.3	$ 8,509.4	$ 7,157.1
OppenheimerFunds Acquisition
$ in millions
Cash and cash equivalents	360.0	360.0
Accounts receivable	133.1	133.1
Investments	178.4	178.4
Prepaid assets	24.8	24.8
Other assets	181.2	181.2
Property, equipment and software, net	104.1	104.1
Intangible assets	5,189.0	5,189.0
Goodwill	1,505.3	1,505.3
Total assets	7,675.9	7,675.9
LIABILITIES
Accrued compensation and benefits	263.9	263.9
Accounts payable and accrued expenses	728.1	728.1
Deferred tax liabilities, net	1,088.0	1,088.0
Total liabilities	2,080.0	2,080.0
Total identifiable net assets	5,595.9	5,595.9
Cash consideration		35.0
Total cash and stock consideration		5,595.9
Common stock | OppenheimerFunds Acquisition
LIABILITIES
Stock and other consideration		1,453.6
Preferred Shares | OppenheimerFunds Acquisition
LIABILITIES
Stock and other consideration	$ 4,000.0	4,010.5
Employee stock-based awards | OppenheimerFunds Acquisition
LIABILITIES
Stock and other consideration		$ 96.8