Derivatives And Risk Management (Schedule Of Derivative Instruments, Notional Amount In BCF, Weighted Average Contract Prices And Fair Value) (Details) - Not Designated as Hedging Instrument [Member] $ in Millions, ft³ in Billions	6 Months Ended
	Jun. 30, 2017 USD ($) $ / MMBTU ft³
Fixed Price Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	168
Average price per MMBtu	3.07
Fair Value | $	$ (2)
Two-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	48
Two-way Costless-collars - 2017 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.93
Two-way Costless-collars - 2017 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.35
Three-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	68
Three-way Costless-collars - 2017 Sold Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.29
Three-way Costless-collars - 2017 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.97
Three-way Costless-collars - 2017 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.30
Financial protection on production - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	284
Fair Value | $	$ (2)
Fixed Price Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	94
Average price per MMBtu	3.00
Fair Value | $	$ 1
Two-way Costless-collars - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	23
Fair Value | $	$ (2)
Two-way Costless-collars - 2018 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.97
Two-way Costless-collars - 2018 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.56
Three-way Costless-collars - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	272
Fair Value | $	$ 9
Three-way Costless-collars - 2018 Sold Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.40
Three-way Costless-collars - 2018 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.97
Three-way Costless-collars - 2018 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.37
Financial protection on production - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	389
Fair Value | $	$ 8
Three-way Costless-collars - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	108
Fair Value | $	$ (2)
Three-way Costless-collars - 2019 Sold Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.50
Three-way Costless-collars - 2019 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.95
Three-way Costless-collars - 2019 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.32
Financial protection on production - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	108
Fair Value | $	$ (2)
Basis Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	86
Basis differential per MMBtu	(1.03)
Fair Value | $	$ (13)
Basis Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	20
Basis differential per MMBtu	(0.95)
Fair Value | $	$ (15)
Basis Swaps [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	106
Fair Value | $	$ (28)
Call Options - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	43
Floor price per MMBtu	3.68
Fair Value | $	$ (2)
Premium paid | $	$ 5
Call Options - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Floor price per MMBtu	3.50
Fair Value | $	$ (11)
Call Options - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Floor price per MMBtu	3.50
Fair Value | $	$ (10)
Call Options - 2020 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Floor price per MMBtu	3.75
Fair Value | $	$ (5)
Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	190
Fair Value | $	$ (28)