Investments (Details 5) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 178,548
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	2,479,316
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	3,868,653
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	4,811,166
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	2,845,197
Available for Sale at Fair value - Amortized cost	14,182,880	13,345,022
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	181,033
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	2,559,352
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	4,195,878
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	6,393,243
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	2,871,444
Fixed maturity securities available-for-sale	$ 16,200,950	$ 14,304,597

This item represents debt securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after five years and through ten years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

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