Derivative Instruments (Open Credit Default Swap Liabilities) (Details) - Credit Default Swap Liabilities [Member] $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) security
Summary Of Credit Derivatives
Maximum potential payout	$ 55
BBB+ [Member]
Summary Of Credit Derivatives
Maturity	Dec. 20, 2024
Credit rating of underlying obligation	BBB+	[1]
Number of instruments | security	1
Fair value	$ 1	[2]
Maximum potential payout	$ 55

[1] Represents average credit ratings based on the midpoint of the applicable ratings among Moody’s, S&P and Fitch Ratings, as scaled to the corresponding S&P ratings.

[2] Broker quotes are used to determine the market value of our credit default swaps.