Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - Private equity funds $ in Millions	Mar. 31, 2018 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 74.2
1-3 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	6.1
3-5 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	6.2
5-10 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	49.2
Greater than 10 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 12.7