Derivative Instruments (Non Hedging Derivatives and Embedded Derivatives Effect on Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ (16,178)	$ 118,527	$ (8,595)	$ 203,098
Policy acquisition costs and other insurance expenses	(300,412)	(409,374)	(577,455)	(764,247)
Interest credited	(77,246)	(115,962)	(197,924)	(226,556)
Other revenues	66,936	120,726	129,223	188,316
Not Designated as Hedging Instrument
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(10,677)	60,213	(46,531)	109,732
Not Designated as Hedging Instrument | Interest Rate Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(41,729)	22,251	(12,385)	51,904
Not Designated as Hedging Instrument | Interest Rate Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	0	2,004	3,275	3,286
Not Designated as Hedging Instrument | Financial Futures
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(2,183)	(7,684)	(9,514)	(9,268)
Not Designated as Hedging Instrument | Foreign Currency Forwards
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(1,433)	1,178	(1,653)	2,332
Not Designated as Hedging Instrument | Consumer Price Index Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	168	114	97	467
Not Designated as Hedging Instrument | Credit Default Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(187)	4,783	2,471	2,669
Not Designated as Hedging Instrument | Equity Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(2,606)	(8,800)	(10,672)	(17,765)
Not Designated as Hedging Instrument | Longevity Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	1,911	0	3,731	0
Not Designated as Hedging Instrument | Mortality Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	(478)	0	(957)	0
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	(23,098)	78,835	(25,423)	156,076
Not Designated as Hedging Instrument | Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Interest credited	8,080	(27,285)	(21,246)	(51,125)
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	$ 50,878	$ (5,183)	$ 25,745	$ (28,844)