Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 0.0	$ 54.6
Hedge Fund, Long/ Short Equity Banks and Financial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 0.0	$ 54.6

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration