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Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - Private equity security $ in Millions	Sep. 30, 2018 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	$ 92.0
1-3 years
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	14.2
3-5 years
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	5.0
5-10 years
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	55.9
Greater than 10 years
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	$ 16.9

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