Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional Amount	$ 9,878,160	$ 8,943,979
Carrying Value / Fair Value of Assets	215,411	101,352
Carrying Value / Fair Value of Liabilities	1,047,236	1,087,331
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	9,075,954	8,166,174
Carrying Value / Fair Value of Assets	163,175	79,449
Carrying Value / Fair Value of Liabilities	1,036,602	1,082,105
Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	1,135,243	1,592,943
Carrying Value / Fair Value of Assets	64,064	32,555
Carrying Value / Fair Value of Liabilities	4,933	21,873
Not Designated as Hedging Instrument | Interest Rate Options
Derivative [Line Items]
Notional Amount	240,000	240,000
Carrying Value / Fair Value of Assets	6,705	2,554
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Financial Futures
Derivative [Line Items]
Notional Amount	215,732	123,780
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	40,000	79,618
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	10,408	12,772
Not Designated as Hedging Instrument | Consumer Price Index Swaps
Derivative [Line Items]
Notional Amount	58,780	59,922
Carrying Value / Fair Value of Assets	32	0
Carrying Value / Fair Value of Liabilities	133	309
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative [Line Items]
Notional Amount	763,700	682,700
Carrying Value / Fair Value of Assets	10,384	10,438
Carrying Value / Fair Value of Liabilities	2,881	2,156
Not Designated as Hedging Instrument | Equity Options
Derivative [Line Items]
Notional Amount	571,236	757,352
Carrying Value / Fair Value of Assets	40,966	33,902
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Longevity Swap [Member]
Derivative [Line Items]
Notional Amount	350,000	0
Carrying Value / Fair Value of Assets	4,407	0
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Mortality Swap [Member]
Derivative [Line Items]
Notional Amount	50,000	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	320	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	36,617	0
Carrying Value / Fair Value of Liabilities	0	176,270
Not Designated as Hedging Instrument | Embedded Derivatives In Indexed Annuity [Member]
Derivative [Line Items]
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	911,549	838,670
Not Designated as Hedging Instrument | Embedded Derivatives In Variable Annuity [Member]
Derivative [Line Items]
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	106,378	30,055
Not Designated as Hedging Instrument | Synthetic Guaranteed Investment Contracts
Derivative [Line Items]
Notional Amount	5,651,263	4,629,859
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	802,206	777,805
Carrying Value / Fair Value of Assets	52,236	21,903
Carrying Value / Fair Value of Liabilities	10,634	5,226
Designated As Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	120,000	49,131
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	10,634	4,606
Designated As Hedging Instrument | Currency Swap [Member]
Derivative [Line Items]
Notional Amount	682,206	728,674
Carrying Value / Fair Value of Assets	52,236	21,903
Carrying Value / Fair Value of Liabilities	$ 0	$ 620