Derivative Instruments (Location and Amounts of Unrealized And Realized Gains (Losses) On Derivatives Recorded In The Condensed Consolidated Income Statements) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ 3.4	$ 15.1	$ (21.8)	$ (3.9)
Foreign exchange (loss) gain
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	3.3	1.2	1.1	(6.2)
Foreign exchange (loss) gain | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	3.3	1.2	1.1	(6.2)
Net realized investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	0.1	13.9	(22.9)	2.3
Net realized investment gains | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(0.4)	(0.3)	(15.3)	0.8
Net realized investment gains | Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ 0.5	$ 14.2	$ (7.6)	$ 1.5