Derivatives And Risk Management (Balance Sheet Classification Of Derivative Financial Instruments) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative assets	$ 35	$ 3
Derivative liabilities	58	5
Basis Swaps [Member] | Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets		3
Fixed Price Swaps [Member] | Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	20
Purchased Put Options [Member] | Derivative Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	15
Sold Call Options [Member] | Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities	5
Sold Call Options [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities	45
Interest Rate Swaps [Member] | Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities	3	3
Interest Rate Swaps [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ 5	$ 2