Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional Amount	$ 9,250,744	$ 8,943,979
Carrying Value / Fair Value of Assets	145,504	101,352
Carrying Value / Fair Value of Liabilities	978,567	1,087,331
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	8,458,620	8,166,174
Carrying Value / Fair Value of Assets	120,908	79,449
Carrying Value / Fair Value of Liabilities	977,459	1,082,105
Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	1,314,868	1,592,943
Carrying Value / Fair Value of Assets	62,348	32,555
Carrying Value / Fair Value of Liabilities	7,413	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	5,840	2,554
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Financial Futures
Derivative [Line Items]
Notional Amount	231,297	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	94,003	79,618
Carrying Value / Fair Value of Assets	313	0
Carrying Value / Fair Value of Liabilities	7,992	12,772
Not Designated as Hedging Instrument | Consumer Price Index Swaps
Derivative [Line Items]
Notional Amount	63,390	59,922
Carrying Value / Fair Value of Assets	69	0
Carrying Value / Fair Value of Liabilities	0	309
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative [Line Items]
Notional Amount	723,700	682,700
Carrying Value / Fair Value of Assets	12,390	10,438
Carrying Value / Fair Value of Liabilities	1,624	2,156
Not Designated as Hedging Instrument | Equity Options
Derivative [Line Items]
Notional Amount	598,564	757,352
Carrying Value / Fair Value of Assets	39,948	33,902
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	20,194	176,270
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	881,337	838,670
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	58,899	30,055
Not Designated as Hedging Instrument | Synthetic Guaranteed Investment Contracts
Derivative [Line Items]
Notional Amount	5,192,798	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	792,124	777,805
Carrying Value / Fair Value of Assets	24,596	21,903
Carrying Value / Fair Value of Liabilities	1,108	5,226
Designated As Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	109,918	49,131
Carrying Value / Fair Value of Assets	1,537	0
Carrying Value / Fair Value of Liabilities	1,108	4,606
Designated As Hedging Instrument | Currency Swap [Member]
Derivative [Line Items]
Notional Amount	682,206	728,674
Carrying Value / Fair Value of Assets	23,059	21,903
Carrying Value / Fair Value of Liabilities	$ 0	$ 620