Derivatives And Risk Management (Narrative) (Details) $ in Millions, ft³ in Billions	9 Months Ended
	Sep. 30, 2015 USD ($) ft³
Derivative [Line Items]
Accumulated other comprehensive income, net gain related to hedging activities | $	$ 31
Deferred income tax liability, accumulated other comprehensive income | $	23
Cash flow hedge after-tax net gain to be transferred from accumulated other comprehensive income to earnings during the next twelve months | $	$ 31
2015 Fixed Price Swaps [Member]
Derivative [Line Items]
Volume of natural gas production	60
Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount | $	$ 170
Not Designated as Hedging Instrument [Member] | 2015 Basis Swaps [Member]
Derivative [Line Items]
Volume of natural gas production	4
Not Designated as Hedging Instrument [Member] | 2016 Basis Swaps [Member]
Derivative [Line Items]
Volume of natural gas production	4
Not Designated as Hedging Instrument [Member] | 2015 Fixed Price Call Options [Member]
Derivative [Line Items]
Volume of natural gas production	50
Not Designated as Hedging Instrument [Member] | 2016 Fixed Price Call Options [Member]
Derivative [Line Items]
Volume of natural gas production	120
Not Designated as Hedging Instrument [Member] | 2015 Fixed Price Swaps [Member]
Derivative [Line Items]
Volume of natural gas production	30
Maximum [Member] | Not Designated as Hedging Instrument [Member] | 2015 Floating Price Swaps [Member]
Derivative [Line Items]
Volume of natural gas production	1