Derivative Financial Instruments (Effect Of Non-Hedging Derivatives On Income Statement And Included In Net Realized Gains (Losses) On Financial Instruments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) Recognized	$ (10.3)	$ (153.8)
Interest Rate Swaps [Member] | Net realized gains (losses) on financial instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) Recognized	0.6	(16.9)
Options [Member] | Net realized gains (losses) on financial instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) Recognized	(10.5)	(136.4)
Futures [Member] | Net realized gains (losses) on financial instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) Recognized	$ (0.4)	$ (0.5)