Derivative Instruments (Open Credit Default Swap Liabilities) (Details) - Open Credit Default Swap Liabilities [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) item
Summary Of Credit Derivatives
Maximum potential payout	$ 52
BBB+ [Member] | 12/20/2022 Maturity [Member]
Summary Of Credit Derivatives
Credit rating of underlying obligation	BBB+	[1]
Number of instruments | item	1
Fair value	$ 1	[2]
Maximum potential payout	$ 52

[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.Credit default swaps were entered into in order to hedge the liability exposure on certain variable annuity products.