Derivative Instruments (Non Hedging Derivatives and Embedded Derivatives Effect on Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 118,264	$ (16,178)	$ (2,622)	$ (8,595)
Policy acquisition costs and other insurance expenses	(405,681)	(300,412)	(639,444)	(577,455)
Interest credited	(95,849)	(77,246)	(183,754)	(197,924)
Other revenues	66,193	66,936	125,376	129,223
Not Designated as Hedging Instrument
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	87,543	(10,677)	(12,151)	(46,531)
Not Designated as Hedging Instrument | Interest Rate Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	41,500	(41,729)	104,027	(12,385)
Not Designated as Hedging Instrument | Interest Rate Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net			0	3,275
Not Designated as Hedging Instrument | Financial Futures
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(7,557)	(2,183)	(18,608)	(9,514)
Not Designated as Hedging Instrument | Foreign Currency Forwards
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	3,577	(1,433)	6,077	(1,653)
Not Designated as Hedging Instrument | Consumer Price Index Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(520)	168	(700)	97
Not Designated as Hedging Instrument | Credit Default Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	3,518	(187)	6,864	2,471
Not Designated as Hedging Instrument | Equity Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(3,225)	(2,606)	(5,928)	(10,672)
Not Designated as Hedging Instrument | Longevity Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	2,394	1,911	2,481	3,731
Not Designated as Hedging Instrument | Mortality Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	1,046	(478)	622	(957)
Not Designated as Hedging Instrument | Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	76,966	(23,098)	(15,283)	(25,423)
Not Designated as Hedging Instrument | Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Interest credited	2,019	8,080	(626)	(21,246)
Not Designated as Hedging Instrument | Embedded Derivatives In Variable Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ (28,137)	$ 50,878	$ (91,077)	$ 25,745