Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 616,796
Due after one year through five years	3,673,274
Due after five year through ten years	7,148,863
Due after ten years	5,788,312
Asset and mortgage-backed securities	3,270,279
Total	20,497,524	20,270,734
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	624,013
Due after one year through five years	3,873,527
Due after five year through ten years	7,474,062
Due after ten years	6,788,627
Asset and mortgage-backed securities	3,396,953
Total	$ 22,157,182	$ 21,474,136