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Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Private equity security |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | $ 105.9 |
Hedge and private equity funds included in other long-term investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 105.9 | $ 161.1
Unfunded Commitments | 44.4 | 50.2
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 0.0 | 54.6
Unfunded Commitments | 0.0 | 0.0
Hedge funds | Hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 0.0 | 54.6
Unfunded Commitments | 0.0 | 0.0
Private equity security | Manufacturing/Industrial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 43.8 | 57.7
Unfunded Commitments | 4.0 | 4.1
Private equity security | Aerospace/Defense/Government |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 44.8 | 33.8
Unfunded Commitments | 15.7 | 23.3
Private equity security | Financial services |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 17.3 | 15.0
Unfunded Commitments | 24.7 | 22.8
Private equity security | Private equity security |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair Value | 105.9 | 106.5
Unfunded Commitments | $ 44.4 | $ 50.2

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