Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional Amount	$ 8,194,538	$ 6,598,107
Carrying Value / Fair Value of Assets	109,819	190,634
Carrying Value / Fair Value of Liabilities	1,037,378	1,209,616
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	7,362,929	5,911,320
Carrying Value / Fair Value of Assets	100,475	190,290
Carrying Value / Fair Value of Liabilities	1,030,283	1,181,432
Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	1,510,467	2,195,059
Carrying Value / Fair Value of Assets	45,280	123,085
Carrying Value / Fair Value of Liabilities	15,694	17,867
Not Designated as Hedging Instrument | Interest Rate Options
Derivative [Line Items]
Notional Amount	240,000	0
Carrying Value / Fair Value of Assets	5,699	0
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Financial Futures
Derivative [Line Items]
Notional Amount	84,192	127,877
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Foreign Currency Forwards
Derivative [Line Items]
Notional Amount	79,618	74,400
Carrying Value / Fair Value of Assets	0	1,017
Carrying Value / Fair Value of Liabilities	8,928	2,105
Not Designated as Hedging Instrument | Consumer Price Index Swaps
Derivative [Line Items]
Notional Amount	76,306	85,135
Carrying Value / Fair Value of Assets	131	1,446
Carrying Value / Fair Value of Liabilities	19	0
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative [Line Items]
Notional Amount	689,700	714,000
Carrying Value / Fair Value of Assets	5,744	2,228
Carrying Value / Fair Value of Liabilities	3,810	5,922
Not Designated as Hedging Instrument | Equity Options
Derivative [Line Items]
Notional Amount	704,402	696,776
Carrying Value / Fair Value of Assets	43,621	62,514
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements
Derivative [Line Items]
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	175,933	243,177
Not Designated as Hedging Instrument | Embedded Derivatives In Indexed Annuity Products
Derivative [Line Items]
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	760,746	740,256
Not Designated as Hedging Instrument | Embedded Derivatives In Variable Annuity Products
Derivative [Line Items]
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	65,153	172,105
Not Designated as Hedging Instrument | Synthetic Guaranteed Investment Contracts
Derivative [Line Items]
Notional Amount	3,978,244	2,018,073
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	0	0
Designated As Hedging Instrument
Derivative [Line Items]
Notional Amount	831,609	686,787
Carrying Value / Fair Value of Assets	9,344	344
Carrying Value / Fair Value of Liabilities	7,095	28,184
Designated As Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	51,335	57,275
Carrying Value / Fair Value of Assets	0	344
Carrying Value / Fair Value of Liabilities	2,770	786
Designated As Hedging Instrument | Foreign Currency Swaps
Derivative [Line Items]
Notional Amount	780,274	629,512
Carrying Value / Fair Value of Assets	9,344	0
Carrying Value / Fair Value of Liabilities	$ 4,325	$ 27,398