Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 802,218
Due after one year through five years	5,606,886
Due after five year through ten years	8,633,420
Due after ten years	9,875,740
Asset and mortgage-backed securities	4,117,010
Total	29,035,274	$ 28,322,977
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	809,704
Due after one year through five years	5,828,982
Due after five year through ten years	8,985,775
Due after ten years	11,345,792
Asset and mortgage-backed securities	4,178,461
Total	$ 31,148,714	$ 29,642,905