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Segment Information - Schedule of Segment Information (Details) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) segment channel | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Segment Reporting [Abstract] |  |  |  |  |
Number of operating segments | segment |  |  | 3 |  |
Number of principal distribution channels | channel |  |  | 3 |  |
Statements of Income |  |  |  |  |
Revenue | $ 544.7 | $ 613.1 | $ 1,644.2 | $ 1,894.7 |
Net income (controlling interest) | 109.2 | 107.7 | 321.1 | 362.0 |
Balance Sheet Information |  |  |  |  |
Total Assets | 8,323.4 |  | 8,323.4 |  | $ 7,769.4
Operating Segments | Institutional |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 215.0 | 236.7 | 662.4 | 745.1 |
Net income (controlling interest) | 51.6 | 51.6 | 162.6 | 158.9 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,840.6 |  | 3,840.6 |  | 3,717.1
Operating Segments | Mutual Fund |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 258.6 | 310.1 | 773.8 | 951.3 |
Net income (controlling interest) | 46.3 | 45.2 | 124.4 | 167.8 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,450.2 |  | 3,450.2 |  | 3,070.5
Operating Segments | High Net Worth |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 71.1 | 66.3 | 208.0 | 198.3 |
Net income (controlling interest) | 11.3 | $ 10.9 | 34.1 | $ 35.3 |
Balance Sheet Information |  |  |  |  |
Total Assets | $ 1,032.6 |  | $ 1,032.6 |  | $ 981.8

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