Derivative Instruments (Non Hedging Derivatives and Embedded Derivatives Effect on Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 7,583us-gaap_GainLossOnInvestments	$ 84,571us-gaap_GainLossOnInvestments
Policy acquisition costs and other insurance expenses	(277,043)	(354,873)
Interest credited	(120,678)	(110,594)
Other revenues	62,287us-gaap_OtherIncome	67,590us-gaap_OtherIncome
Not Designated as Hedging Instrument
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(35,854)	49,517
Not Designated as Hedging Instrument \| Interest Rate Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	29,344	29,653
Not Designated as Hedging Instrument \| Interest Rate Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	3,275	1,282
Not Designated as Hedging Instrument \| Financial Futures
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(7,331)	(1,584)
Not Designated as Hedging Instrument \| Foreign Currency Forwards
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(220)	1,154
Not Designated as Hedging Instrument \| Consumer Price Index Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(71)	352
Not Designated as Hedging Instrument \| Credit Default Swaps
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	2,658	(2,114)
Not Designated as Hedging Instrument \| Equity Options
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(8,067)	(8,966)
Not Designated as Hedging Instrument \| Longevity Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	1,821	0
Not Designated as Hedging Instrument \| Mortality Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Other revenues	(479)	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	(2,325)	77,241
Not Designated as Hedging Instrument \| Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Interest credited	(29,326)	(23,840)
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	$ (25,133)	$ (23,661)

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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