Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional Amount	$ 9,056,525	$ 8,943,979
Carrying Value / Fair Value of Assets	134,216	101,352
Carrying Value / Fair Value of Liabilities	1,037,624	1,087,331
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	8,323,276	8,166,174
Carrying Value / Fair Value of Assets	90,003	79,449
Carrying Value / Fair Value of Liabilities	1,033,569	1,082,105
Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	1,330,276	1,592,943
Carrying Value / Fair Value of Assets	46,649	32,555
Carrying Value / Fair Value of Liabilities	10,978	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	3,836	2,554
Carrying Value / Fair Value of Liabilities	0	0
Not Designated as Hedging Instrument | Financial Futures
Derivative [Line Items]
Notional Amount	143,629	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	68,885	79,618
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	10,067	12,772
Not Designated as Hedging Instrument | Consumer Price Index Swaps
Derivative [Line Items]
Notional Amount	62,254	59,922
Carrying Value / Fair Value of Assets	13	0
Carrying Value / Fair Value of Liabilities	83	309
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative [Line Items]
Notional Amount	663,700	682,700
Carrying Value / Fair Value of Assets	8,639	10,438
Carrying Value / Fair Value of Liabilities	1,425	2,156
Not Designated as Hedging Instrument | Equity Options
Derivative [Line Items]
Notional Amount	821,432	757,352
Carrying Value / Fair Value of Assets	30,866	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	99,029	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	858,270	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	53,717	30,055
Not Designated as Hedging Instrument | Synthetic Guaranteed Investment Contracts
Derivative [Line Items]
Notional Amount	4,993,100	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	733,249	777,805
Carrying Value / Fair Value of Assets	44,213	21,903
Carrying Value / Fair Value of Liabilities	4,055	5,226
Designated As Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional Amount	51,043	49,131
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	4,055	4,606
Designated As Hedging Instrument | Foreign Currency Swaps
Derivative [Line Items]
Notional Amount	682,206	728,674
Carrying Value / Fair Value of Assets	44,213	21,903
Carrying Value / Fair Value of Liabilities	$ 0	$ 620