Derivative Financial Instruments (Offsetting Of Derivative Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative assets, Gross Amount of Recognized Assets (Liabilities)	$ 68.7	$ 111.6
Derivative assets, Gross Amount Offset in the Consolidated Balance Sheet	0.0	0.0
Derivative assets, Net Amount Presented in the Consolidated Balance Sheet	68.7	111.6
Derivative assets, Gross Amounts not offset in the Consolidated Balance Sheet, Derivative Financial Instruments	(18.7)	(30.9)
Derivative assets, Gross Amounts not offset in the Consolidated Balance Sheet, Cash Collateral Pledged/(Received)	(8.4)	(48.7)
Derivative assets, Gross Amounts not offset in the Consolidated Balance Sheet, Net Amount	41.6	32.0
Derivative liabilities, Gross Amount of Recognized Assets (Liabilities)	(87.0)	(68.8)
Derivative liabilities, Gross Amount Offset in the Consolidated Balance Sheet	0.0	0.0
Derivative Liability, Net Amount Presented in the Consolidated Balance Sheet	(87.0)	(68.8)
Derivative liabilities, Gross Amounts not offset in the Consolidated Balance Sheet, Derivative Financial Instruments	18.7	30.9
Derivative liabilities, Gross Amounts not offset in the Consolidated Balance Sheet, Cash Collateral Pledged/(Received)	23.0	5.0
Derivative liabilities, Gross Amounts not offset in the Consolidated Balance Sheet, Net Amount	$ (45.3)	$ (32.9)