Derivative Instruments (Non Hedging Derivatives and Embedded Derivatives Effect on Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 86,624	$ (111,346)	$ 84,002	$ (119,941)
Policy acquisition costs and other insurance expenses	(300,962)	(249,702)	(940,406)	(827,157)
Interest credited	(116,848)	(34,008)	(300,602)	(231,932)
Other revenues	72,468	71,038	197,844	200,261
Not Designated as Hedging Instrument
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	31,535	(23,464)	19,384	(69,997)
Not Designated as Hedging Instrument | Interest Rate Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	4,122	42,014	108,149	29,629
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	(11,677)	16,654	(30,285)	7,141
Not Designated as Hedging Instrument | Foreign Currency Forwards
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	507	708	6,584	(946)
Not Designated as Hedging Instrument | Consumer Price Index Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	76	(250)	(624)	(153)
Not Designated as Hedging Instrument | Credit Default Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	6,672	(8,407)	13,536	(5,936)
Not Designated as Hedging Instrument | Equity Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(13,648)	15,150	(19,576)	4,477
Not Designated as Hedging Instrument | Longevity Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	8,921	2,404	11,402	6,136
Not Designated as Hedging Instrument | Mortality Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	(400)	(442)	222	(1,399)
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	49,078	(46,169)	33,795	(71,592)
Not Designated as Hedging Instrument | Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Interest credited	20,104	50,246	(20,730)	28,999
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	$ 7,988	$ (95,372)	$ (83,089)	$ (69,628)