Investments (Fixed Maturity Securities Pledged And Received As Collateral) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 17,926,454	$ 17,575,507
Available-for-sale Securities	18,512,048	17,708,156
Collateral Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	192,718	169,678
Available-for-sale Securities	204,980	176,782
Collateral Received Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	261,601	242,914
Reported Value Measurement [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets Held-in-trust	10,698,579	10,535,729
Estimate of Fair Value Measurement [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets Held-in-trust	$ 11,345,193	$ 10,928,393