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	3 Months Ended
	Mar. 31, 2017 USD ($) $ / MMBTU ft³
Fixed Price Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	262
Average price per MMBtu	3.07
Fair value | $	$ (58)
Two-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	65
Fair value | $	$ (11)
Two-way Costless-collars - 2017 Purchased Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.92
Two-way Costless-collars - 2017 Sold Calls [Member]
Derivative [Line Items]
Cap price per MMBtu	3.34
Three-way Costless-collars - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	102
Fair value | $	$ (16)
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
Basis Swaps - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	138
Basis differential per MMBtu	(1.04)
Fair value | $	$ (73)
Financial protection on production - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	567
Fair value | $	$ (158)
Fixed Price Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	68
Average price per MMBtu	3.02
Fair value | $	$ (1)
Two-way Costless-collars - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	23
Fair value | $	$ (6)
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	245
Fair value | $	$ (6)
Three-way Costless-collars - 2018 Sold Puts [Member]
Derivative [Line Items]
Floor price per MMBtu	2.39
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
Basis Swaps - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	20
Basis differential per MMBtu	(0.95)
Fair value | $	$ (15)
Financial protection on production - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	356
Fair value | $	$ (28)
Three-way Costless-collars - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	99
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	3.31
Financial protection on production - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	99
Fair value | $	$ (2)
Sold Call Options - 2017 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	64
Floor price per MMBtu	3.54
Fair value | $	$ (10)
Premium paid | $	$ 5
Sold Call Options - 2018 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Floor price per MMBtu	3.50
Fair value | $	$ (14)
Sold Call Options - 2019 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Floor price per MMBtu	3.50
Fair value | $	$ (10)
Sold Call Options - 2020 [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Floor price per MMBtu	3.75
Fair value | $	$ (5)
Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	211
Fair value | $	$ (39)