Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 31,963	$ 29,205
Available-for-sale Securities	36,208	31,393
JAPAN
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,493	813
Available-for-sale Securities	1,491	852
Canadian Province Of Ontario Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,303	1,205
Available-for-sale Securities	2,474	2,163
Canadian Province Of Quebec Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,054	1,014
Available-for-sale Securities	$ 1,528	$ 1,379