Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative [Line Items]
Gas sales	$ 251	$ 457	$ 566	$ 1,082
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative liabilities	8		8		$ 5
Fixed Price Swaps [Member]
Derivative [Line Items]
Derivative liabilities	41		41
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative liabilities	8		8
Notional amount	170		$ 170
Derivative, expiration			Jun. 30, 2020
Designated as Hedging Instrument [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Derivative gain (loss) in other comprehensive income		(3)		21
Gas sales		$ 53		$ 95
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative liabilities	$ 123		$ 123