Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Derivative [Line Items]
Gas sales	$ 315	$ 625
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative liabilities	8		$ 5
Fixed Price Swaps [Member]
Derivative [Line Items]
Accumulated other comprehensive income		24
Gas sales		$ 42
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount	$ 170
Derivative, expiration	Jun. 30, 2020
Natural Gas [Member]
Derivative [Line Items]
Derivative liabilities	$ 15