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Segment Information - Schedule of Segment Information (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2015 USD ($) | Jun. 30, 2014 USD ($) | Jun. 30, 2015 USD ($) Segment Channel | Jun. 30, 2014 USD ($) | Dec. 31, 2014 USD ($)
Segment Reporting [Abstract] |  |  |  |  |
Number of operating segments | Segment |  |  | 3 |  |
Number of principal distribution channels | Channel |  |  | 3 |  |
Statements of Income |  |  |  |  |
Revenue | $ 646.6 | $ 636.3 | $ 1,281.6 | $ 1,229.4 |
Net income (controlling interest) | 128.7 | 99.1 | 256.7 | 176.2 |
Balance Sheet Information |  |  |  |  |
Total Assets | 7,678.8 |  | 7,678.8 |  | $ 7,698.1
Operating Segments | Institutional |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 255.4 | 265.2 | 508.3 | 510.1 |
Net income (controlling interest) | 59.6 | 48.4 | 108.3 | 84.3 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,512.2 |  | 3,512.2 |  | 3,739.8
Operating Segments | Mutual Fund |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 323.0 | 310.0 | 641.3 | 601.9 |
Net income (controlling interest) | 56.1 | 41.2 | 123.8 | 75.3 |
Balance Sheet Information |  |  |  |  |
Total Assets | 3,246.8 |  | 3,246.8 |  | 3,082.0
Operating Segments | High Net Worth |  |  |  |  |
Statements of Income |  |  |  |  |
Revenue | 68.2 | 61.1 | 132.0 | 117.4 |
Net income (controlling interest) | 13.0 | $ 9.5 | 24.6 | $ 16.6 |
Balance Sheet Information |  |  |  |  |
Total Assets | $ 919.8 |  | $ 919.8 |  | $ 876.3

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