Investments (Fair Value Below Amortized Cost of Gross Unrealized Losses for Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 110	$ 748
Percentage Of Total Gross Unrealized Losses	100.00%	100.00%
Less Than 20 Percent [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 76	$ 721
Percentage Of Total Gross Unrealized Losses	69.10%	96.40%
More Than Or Equal To 20 Percent For Less Than Six Months [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 20	$ 21
Percentage Of Total Gross Unrealized Losses	18.20%	2.80%
More Than Or Equal To 20 Percent For Six Months Or Greater [Member]
Gross unrealized losses with number of securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 14	$ 6
Percentage Of Total Gross Unrealized Losses	12.70%	0.80%