Investments (Details Of Company Investments) (Details) - USD ($) $ in Millions |
Sep. 30, 2017 |
Dec. 31, 2016 |
---|---|---|
Investment Holdings [Line Items] | ||
Available for sale investments | $ 90.9 | $ 154.0 |
Equity method investments | 296.5 | 279.0 |
Foreign time deposits | 27.5 | 26.9 |
Cost Method Investments | 6.1 | 5.8 |
Investments | 690.9 | 795.3 |
Seed Money [Member] | ||
Investment Holdings [Line Items] | ||
Available for sale investments | 74.5 | 127.9 |
Trading investments | 160.7 | 121.9 |
Collateralized Loan Obligations [Member] | ||
Investment Holdings [Line Items] | ||
Available for sale investments | 6.7 | 12.9 |
Other Debt Obligations [Member] | ||
Investment Holdings [Line Items] | ||
Available for sale investments | 9.7 | 13.2 |
Deferred Compensation Arrangements [Member] | ||
Investment Holdings [Line Items] | ||
Trading investments | 89.6 | 170.5 |
Common Stock [Member] | ||
Investment Holdings [Line Items] | ||
Trading investments | 17.9 | 30.4 |
UIT-Related Equity And Debt Securities [Member] | ||
Investment Holdings [Line Items] | ||
Trading investments | $ 1.7 | $ 6.8 |