Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 17,575,507	$ 14,010,604
Available-for-sale Securities	17,708,156	14,885,583
Canadian Province Of Ontario Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	864,444	979,908
Available-for-sale Securities	1,199,080	1,359,339
Canadian Province Of Quebec Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	943,484	1,006,315
Available-for-sale Securities	$ 1,525,903	$ 1,599,673