Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 15,801,362	$ 14,010,604
Available-for-sale Securities	16,173,447	14,885,583
Canadian Province Of Quebec Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	966,171	1,006,315
Available-for-sale Securities	1,464,067	1,599,673
Canadian Province Of Ontario Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	876,694	979,908
Available-for-sale Securities	$ 1,209,125	$ 1,359,339