Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 29,205	$ 24,006
Available-for-sale Securities	31,393	23,982
Canadian Province Of Ontario Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,205	1,091
Available-for-sale Securities	2,163	1,757
Canadian Province Of Quebec Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,014	914
Available-for-sale Securities	$ 1,379	$ 1,188