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, 2016 USD ($) $ / MMBTU ft³
2016 [Member] | Fixed Price Swaps [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	64
Average fixed price per MMBtu | $ / MMBTU	2.48
Fair value | $	$ 20
2016 [Member] | Purchased Put Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	43
Floor price per MMBtu | $ / MMBTU	2.35
Fair value | $	$ 15
2016 [Member] | Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	90
Cap price per MMBtu | $ / MMBTU	5.00
Fair value | $
2017 [Member] | Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	86
Cap price per MMBtu | $ / MMBTU	3.25
Fair value | $	$ (16)
2018 [Member] | Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	63
Cap price per MMBtu | $ / MMBTU	3.50
Fair value | $	$ (12)
2019 [Member] | Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	52
Cap price per MMBtu | $ / MMBTU	3.50
Fair value | $	$ (13)
2020 [Member] | Sold Call Options [Member]
Derivative [Line Items]
Volume (Bcf) | ft³	32
Cap price per MMBtu | $ / MMBTU	3.75
Fair value | $	$ (9)