Derivative Instruments (Open Credit Default Swap Liabilities) (Details) (Open Credit Default Swap Liabilities [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 item		Dec. 31, 2013 item
Summary Of Credit Derivatives
Credit default swaps, number of instruments	6		6
Fair Value of open credit default swap liabilities	$ (3)	[1]	$ (2)	[1]
Maximum potential payout of open credit default swap liabilities	126		126
BBB- average credit rating | 12/20/2016 maturity
Summary Of Credit Derivatives
Credit rating of underlying obligation	BBB-	[2]	BBB-	[2]
Credit default swaps, number of instruments	3		3
Fair Value of open credit default swap liabilities	(2)	[1]	(1)	[1]
Maximum potential payout of open credit default swap liabilities	68		68
BBB- average credit rating | 3/20/2017 maturity
Summary Of Credit Derivatives
Credit rating of underlying obligation	BBB-	[2]	BBB-	[2]
Credit default swaps, number of instruments	3		3
Fair Value of open credit default swap liabilities	(1)	[1]	(1)	[1]
Maximum potential payout of open credit default swap liabilities	$ 58		$ 58

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

[2] 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.