Derivative Instruments (Schedule Of Unrealized And Realized Gains (Losses) On Derivatives Recorded In The Consolidated Income Statement) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (27,060)		$ (47,470)
Foreign Exchange Contracts [Member] | Investment Portfolio [Member] | Net Realized Investment Losses [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(5,343)		(4,620)
Interest Rate Futures [Member] | Investment Portfolio [Member] | Net Realized Investment Losses [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(37,942)		(54,201)
Investment Portfolio [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(43,285)		(58,821)
Foreign Exchange Contracts [Member] | Operating Activities [Member] | Foreign Exchange (Losses) Gains [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(8,075)	4,832	(5,474)	3,420
Operating Activities [Member] | Net Realized Investment Losses [Member] | Treasury Yield Hedge [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				(3,958)
Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (51,360)	$ 4,832	$ (64,295)	$ (538)