Derivative Instruments (Non Hedging Derivatives and Embedded Derivatives Effect on Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 186,193	$ 63,990	$ 254,136
Other revenues	334,456	300,471	243,973
Gain Loss On Investments Related To Change In Fair Value Of Derivatives Excluding Embedded Derivatives	80,661	(177,258)	(61,446)
Policy Acquisition Costs And Other Insurance Expenses	(1,391,433)	(1,300,780)	(1,306,470)
Interest credited	(451,031)	(476,514)	(379,915)
Not Designated as Hedging Instrument [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	44,958	(80,440)	127,742
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	94,848	(84,398)	16,028
Not Designated as Hedging Instrument [Member] | Interest Rate Options [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	15,641	(11,518)	0
Not Designated as Hedging Instrument [Member] | Future [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(9,550)	(11,157)	(20,245)
Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(8,691)	(13,201)	(5,644)
Not Designated as Hedging Instrument [Member] | Consumer Price Index Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(344)	(1,942)	(267)
Not Designated as Hedging Instrument [Member] | Credit Default Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	3,938	24,188	18,359
Not Designated as Hedging Instrument [Member] | Equity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(22,472)	(79,230)	(69,677)
Not Designated as Hedging Instrument [Member] | Longevity Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	8,088	0	0
Not Designated as Hedging Instrument [Member] | Mortality Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	(797)	0	0
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	198,365	70,177	115,009
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Policy Acquisition Costs And Other Insurance Expenses	0	0	(630)
Interest credited	(104,844)	(115,409)	(29,804)
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Variable Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ (129,224)	$ 142,050	$ 104,613