Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Mar. 31, 2019 USD ($) fund	Dec. 31, 2018 USD ($)
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Number of investments	12
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Number of investments	1
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Largest single fund investment | $	$ 53.1	$ 54.3