Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 728,318
Due after one year through five years	6,519,471
Due after five year through ten years	8,991,047
Due after ten years	9,820,871
Asset and mortgage-backed securities	4,038,189
Total	30,097,896	$ 28,322,977
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	733,750
Due after one year through five years	6,847,608
Due after five year through ten years	9,689,531
Due after ten years	12,096,231
Asset and mortgage-backed securities	4,169,299
Total	$ 33,536,419	$ 29,642,905