Derivative Instruments (Open Credit Default Swap Liabilities) (Details) - Open Credit Default Swap Liabilities [Member] $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2018	Dec. 31, 2017 USD ($) item
Summary Of Credit Derivatives
Number of instruments | item			1
Fair value	[1]		$ 1
Maximum potential payout			$ 52
Maturity 12/20/2022 [Member]
Summary Of Credit Derivatives
Maturity	[2]	Dec. 20, 2022
Credit rating of underlying obligation	[3]		BBB+
Number of instruments | item			1
Fair value	[1]		$ 1
Maximum potential payout			$ 52

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

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

[3] 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.