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, 2016 USD ($) $ / MMBTU ft³
Fixed Price Swaps -2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	61
Average price per MMBtu	2.57
Fair value | $	$ (24)
Purchased Put Options - 2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	17
Floor price per MMBtu	2.34
Fair value | $
Two-way Costless-collars - 2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	12
Fair value | $	$ (1)
Two-way Costless-collars - 2016 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.76
Two-way Costless-collars - 2016 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.35
Basis Swap - 2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	7
Average price per MMBtu	0.36
Fair value | $	$ 5
Financial protection on production - 2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	97
Fair value | $	$ (20)
Fixed Price Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	144
Average price per MMBtu	3.07
Fair value | $	$ (16)
Two-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	47
Fair value | $	$ (4)
Two-way Costless-collars - 2017 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.90
Two-way Costless-collars - 2017 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.33
Three-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	18
Fair value | $	$ (2)
Three-way Costless-collars - 2017 Sold Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.25
Three-way Costless-collars - 2017 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.75
Three-way Costless-collars - 2017 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.56
Basis Swap - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	15
Average price per MMBtu	0.02
Fair value | $	$ (6)
Financial protection on production - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	224
Fair value | $	$ (28)
Sold Call Options - 2016 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	60
Cap price per MMBtu	5.00
Fair value | $
Sold Call Options - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	86
Cap price per MMBtu	3.25
Fair value | $	$ (30)
Sold Call Options - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Cap price per MMBtu	3.50
Fair value | $	$ (18)
Sold Call Options - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Cap price per MMBtu	3.50
Fair value | $	$ (17)
Sold Call Options - 2020 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Cap price per MMBtu	3.75
Fair value | $	$ (10)
Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	293
Fair value | $	$ (75)