Investments (Exposure To Concentrations Of Credit Risk) (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
Canadian Province Of Quebec Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,013,019	943,484
Available-for-sale Securities	1,702,423	1,525,903
Canadian Province Of Ontario Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	892,870	864,444
Available-for-sale Securities	$ 1,257,794	$ 1,199,080