Fair Value Of Assets And Liabilities - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign time deposits	$ 27.3	$ 32.0
Equity method investments	355.1	350.8
Other investments	$ 11.9	14.2
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed growth rate of Assets under Management (percent)	0.00%
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	$ 2,407.0	$ 2,080.3
Total Return Swap | Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative notional amount	256.5
Market valuation loss recognized	(1.3)
OppenheimerFunds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability acquired	$ 9.9
OppenheimerFunds | Assumed growth rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inputs used to determine liability (percent)	0
OppenheimerFunds | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inputs used to determine liability (percent)	0.107
Other Digital Wealth Acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability acquired	$ 7.0