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Segment Information - Schedule of Segment Information (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 USD ($) | Jun. 30, 2015 USD ($) | Jun. 30, 2016 USD ($) segment channel | Jun. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Segment Reporting [Abstract] |  |  |  |  |
Number of operating segments | segment |  |  | 3 |  |
Number of principal distribution channels | channel |  |  | 3 |  |
Statements of Income |  |  |  |  |
Revenue | $ 554.1 | $ 646.6 | $ 1,099.5 | $ 1,281.6 |
Net income (controlling interest) | 107.4 | 128.7 | 212.0 | 256.7 |
Balance Sheet Information |  |  |  |  |
Total Assets | 8,034.7 |  | 8,034.7 |  | $ 7,769.4
Operating Segments | Institutional |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 220.1 | 255.4 | 447.4 | 508.3 |
Net income (controlling interest) | 51.1 | 59.6 | 111.0 | 108.3 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,676.1 |  | 3,676.1 |  | 3,717.1
Operating Segments | Mutual Fund |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 264.9 | 323.0 | 515.2 | 641.3 |
Net income (controlling interest) | 44.8 | 56.1 | 78.1 | 123.8 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,362.8 |  | 3,362.8 |  | 3,070.5
Operating Segments | High Net Worth |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 69.1 | 68.2 | 136.9 | 132.0 |
Net income (controlling interest) | 11.5 | $ 13.0 | 22.9 | $ 24.6 |
Balance Sheet Information |  |  |  |  |
Total Assets | $ 995.8 |  | $ 995.8 |  | $ 981.8

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