Securities Sold Under Agreements To Repurchase (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities sold under agreements to repurchase average	$ 316.1	$ 333.9	$ 321.1
Securities sold under agreements to repurchase maximum outstanding	$ 334.9	$ 360.2	$ 334.6