Fair Value Of Assets And Liabilities (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign time deposits	$ 29.9	$ 32.0
Equity method investments	426.1	350.8
Other investments	10.5	14.2
Put option contracts, purchases		3.9
Contingent consideration	18.6	60.2
Designated as Hedging Instrument | Foreign Exchange Option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative gain (loss) , net	0.1	(4.8)
Designated as Hedging Instrument | Total Return Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative gain (loss) , net	39.8	16.8
Notional value of futures contracts	279.3
Derivative asset	5.1
Not Designated as Hedging Instrument | Total Return Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional value of futures contracts		145.9
Foreign exchange hedge gain	0.8	9.9
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign time deposits	29.9	$ 32.0
Deutsche Bank
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	5.9
OppenheimerFunds Acquisition
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ 8.4
OppenheimerFunds Acquisition | Measurement Input, Long-term Revenue Growth Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (percent)	0
OppenheimerFunds Acquisition | Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (percent)	0.107