Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($) fund	Dec. 31, 2018 USD ($)
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Number of investments \| fund	1
Hedge funds \| Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 54.8	$ 54.3
Investment redemption, notice period	45 days
Hedge funds \| Hedge Fund, Long/ Short Equity Banks and Financial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 54.8	$ 54.3

Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

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