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 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	$ (1.1)	$ (19.7)	$ (22.9)	$ (23.6)
Foreign exchange gain (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	(0.1)	0.2	1.0	(6.0)
Foreign exchange gain (loss) | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	(0.1)	0.2	1.0	(6.0)
Net realized investment gains (losses)
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	(1.0)	(19.9)	(23.9)	(17.6)
Net realized investment gains (losses) | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	0.0	0.1	(15.3)	0.9
Net realized investment gains (losses) | Interest rate futures and swaps
Derivative Instruments, Gain (Loss) [Line Items]
Realized and unrealized gains (losses) on derivatives	$ (1.0)	$ (20.0)	$ (8.6)	$ (18.5)