Derivatives And Risk Management (Schedule Of Derivative Instruments, Notional Amount In BCF, Weighted Average Contract Prices And Fair Value) (Details) $ in Millions, ft³ in Billions	9 Months Ended
	Sep. 30, 2016 USD ($) $ / MMBTU ft³
Derivative [Line Items]
Cap price per MMBtu
Fixed Price Swaps -2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	51
Average price per MMBtu	2.81
Fair value | $	$ (8)
Purchased Put Options - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	4
Floor price per MMBtu	2.34
Fair value | $
Two-way Costless-collars - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	40
Fair value | $	$ 2
Two-way Costless-collars - 2016 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.93
Two-way Costless-collars - 2016 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.33
Three-way Costless-collars - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	5
Fair value | $
Three-way Costless-collars - 2016 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	3.00
Three-way Costless-collars - 2016 Sold Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.30
Three-way Costless-collars - 2016 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.25
Basis Swap - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	16
Basis differential per MMBtu	0.02
Fair value | $	$ 18
Financial protection on production - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	116
Fair value | $	$ 12
Fixed Price Swaps - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	296
Average price per MMBtu	3.04
Fair value | $	$ (9)
Two-way Costless-collars - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	103
Fair value | $	$ (1)
Two-way Costless-collars - 2017 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.94
Two-way Costless-collars - 2017 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.38
Three-way Costless-collars - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	135
Fair value | $	$ (5)
Three-way Costless-collars - 2017 Sold Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.29
Three-way Costless-collars - 2017 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.97
Three-way Costless-collars - 2017 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.30
Basis Swap - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	76
Basis differential per MMBtu	(0.59)
Fair value | $	$ 13
Financial protection on production - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	610
Fair value | $	$ (2)
Two-way Costless-collars - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	14
Fair value | $	$ (1)
Two-way Costless-collars - 2018 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	3.00
Two-way Costless-collars - 2018 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.46
Three-way Costless-collars - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	73
Fair value | $	$ 4
Three-way Costless-collars - 2018 Sold Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.28
Three-way Costless-collars - 2018 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.93
Three-way Costless-collars - 2018 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.37
Basis Swap - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	2
Basis differential per MMBtu	0.83
Fair value | $	$ (1)
Financial protection on production - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	89
Fair value | $	$ 2
Sold Call Options - 2016 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	30
Cap price per MMBtu	5.00
Fair value | $
Sold Call Options - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	86
Cap price per MMBtu	3.25
Fair value | $	$ (23)
Sold Call Options - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Cap price per MMBtu	3.50
Fair value | $	$ (13)
Sold Call Options - 2019 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Cap price per MMBtu	3.50
Fair value | $	$ (11)
Sold Call Options - 2020 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Cap price per MMBtu	3.75
Fair value | $	$ (7)
Sold Call Options [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	263
Fair value | $	$ (54)