Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 18,417,375	$ 17,575,507
Available-for-sale Securities	19,543,237	17,708,156
Canadian Province Of Quebec Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,026,507	943,484
Available-for-sale Securities	1,854,422	1,525,903
Canadian Province Of Ontario Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	853,014	864,444
Available-for-sale Securities	$ 1,257,954	$ 1,199,080