Fair Value Of Assets And Liabilities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	May 24, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign time deposits	$ 25.8	$ 32.0
Equity method investments	373.0	350.8
Other investments	$ 11.6	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	$ 2,588.8	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	215.3
Market valuation loss recognized	$ (31.4)
OppenheimerFunds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liability acquired			$ 13.6
OppenheimerFunds | Assumed growth rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inputs used to determine liability (percent)	0.04
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		$ 10.5