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	12 Months Ended
	Dec. 31, 2016 USD ($) $ / MMBTU ft³
Fixed Price Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	322
Fixed Price Swaps - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Average price per MMBtu	3.07
Fair value | $	$ (175)
Two-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	103
Two-way Costless-collars - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (42)
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]
Derivative [Line Items]
Volume (Bcf) | ft³	135
Three-way Costless-collars - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (59)
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 Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	132
Basis Swaps - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Basis differential per MMBtu	(0.87)
Fair value | $	$ 19
Financial protection on production - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	692
Financial protection on production - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (257)
Fixed Price Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	18
Fixed Price Swaps - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Average price per MMBtu	3.00
Fair value | $	$ (2)
Two-way Costless-collars - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	14
Two-way Costless-collars - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (6)
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]
Derivative [Line Items]
Volume (Bcf) | ft³	208
Three-way Costless-collars - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (20)
Three-way Costless-collars - 2018 Sold Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.37
Three-way Costless-collars - 2018 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.96
Three-way Costless-collars - 2018 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.37
Basis Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	16
Basis Swaps - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Basis differential per MMBtu	(0.94)
Fair value | $	$ (4)
Financial protection on production - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	256
Financial protection on production - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (32)
Three-way Costless-collars - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	62
Three-way Costless-collars - 2019 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (2)
Three-way Costless-collars - 2019 Sold Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.50
Three-way Costless-collars - 2019 Purchased Puts [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Floor price per MMBtu	2.92
Three-way Costless-collars - 2019 Sold Calls [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.35
Financial protection on production - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	62
Financial protection on production - 2019 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (2)
Sold Call Options - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	86
Sold Call Options - 2017 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.25
Fair value | $	$ (46)
Sold Call Options - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Sold Call Options - 2018 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.50
Fair value | $	$ (18)
Sold Call Options - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Sold Call Options - 2019 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.50
Fair value | $	$ (11)
Sold Call Options - 2020 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Sold Call Options - 2020 [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap price per MMBtu	3.75
Fair value | $	$ (6)
Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	233
Sold Call Options [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value | $	$ (81)