Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 1,409,578
Due after one year through five years	8,141,200
Due after five year through ten years	8,933,926
Due after ten years	15,085,928
Asset and mortgage-backed securities	5,617,995
Total	39,188,627	$ 38,882,168
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	1,419,110
Due after one year through five years	8,340,166
Due after five year through ten years	9,345,621
Due after ten years	16,965,628
Asset and mortgage-backed securities	5,667,918
Total	$ 41,738,443	$ 39,992,346

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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