Investments (Exposure To Concentrations Of Credit Risk) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Document Period End Date	Jun. 30, 2021
Government Of Japan [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 2,890	$ 1,493
Available-for-sale Securities	2,879	1,491
Canadian Province Of Quebec Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,097	1,054
Available-for-sale Securities	1,477	1,528
Canadian Province Of Ontario Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,372	1,303
Available-for-sale Securities	$ 2,315	$ 2,474