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
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ (3.9)	$ (21.0)
Foreign exchange (loss) gain
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	0.8	2.3
Foreign exchange (loss) gain | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	0.8	2.3
Net realized investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(4.0)	(22.9)
Net realized investment gains | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(0.8)	(14.9)
Net realized investment gains | Interest rate swaps and futures
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(3.2)	(8.0)
Other Operating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(0.7)	(0.4)
Other Operating Income (Expense) [Member] | Insurance contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(0.9)	0.0
Other Operating Income (Expense) [Member] | Reinsurance contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ 0.2	$ (0.4)