Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 416,152
Due after one year through five years	3,712,227
Due after five year through ten years	6,800,712
Due after ten years	5,810,710
Asset and mortgage-backed securities	3,177,549
Total	19,917,350	19,559,432
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	421,874
Due after one year through five years	3,890,251
Due after five year through ten years	7,027,350
Due after ten years	6,659,403
Asset and mortgage-backed securities	3,290,230
Total	$ 21,289,108	$ 22,291,614