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Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Private equity security |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | $ 111.3 |
Hedge and private equity funds included in other long-term investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 166.1 | $ 146.1
Unfunded Commitments | 72.6 | 76.7
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 54.8 | 54.3
Unfunded Commitments | 0.0 | 0.0
Hedge funds | Hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 54.8 | 54.3
Unfunded Commitments | 0.0 | 0.0
Private equity security | Manufacturing/Industrial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 53.2 | 42.9
Unfunded Commitments | 4.1 | 10.5
Private equity security | Aerospace/Defense/Government |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 32.4 | 27.6
Unfunded Commitments | 26.9 | 34.9
Private equity security | Direct lending |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 14.5 | 13.0
Unfunded Commitments | 15.0 | 17.7
Private equity security | Financial services |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 11.2 | 8.3
Unfunded Commitments | 26.6 | 13.6
Private equity security | Private equity security |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 111.3 | 91.8
Unfunded Commitments | $ 72.6 | $ 76.7

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