Derivative Instruments and Hedging Activities (Details) (USD $)	3 Months Ended	9 Months Ended
	Mar. 31, 2011	Sep. 30, 2012		Feb. 15, 2011
Derivative Instruments and Hedging Activities [Abstract]
Amount of Gain (Loss) on Derivative Instruments Recognized in Other Comprehensive (Income) Loss	$ 23,000,000
Net liability position of settled interest rate swap				40,000,000
AOCL amount, net of tax, to be reclassified to interest expense over the life of the debt		26,000,000
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		2,000,000
Crude Oil Commodity Contract | Swaps 1
Derivative [Line Items]
Period		2012
Index		NYMEX WTI  (1)	[1]
Volume Per Day		5,000
Weighted Average Fixed Price		91.84
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Swaps 2
Derivative [Line Items]
Period		2012
Index		Dated Brent
Volume Per Day		8,000
Weighted Average Fixed Price		89.06
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Three Way Collars 1
Derivative [Line Items]
Period		2012
Index		NYMEX WTI	[1]
Volume Per Day		23,000
Weighted Average Fixed Price
Weighted Average Short Put Price		61.09
Weighted Average Floor Price		83.04
Weighted Average Ceiling Price		101.66
Crude Oil Commodity Contract | Three Way Collars 2
Derivative [Line Items]
Period		2012
Index		Dated Brent
Volume Per Day		3,000
Weighted Average Fixed Price
Weighted Average Short Put Price		70.00
Weighted Average Floor Price		95.83
Weighted Average Ceiling Price		105.00
Crude Oil Commodity Contract | Swaps 3
Derivative [Line Items]
Period		2013
Index		NYMEX WTI	[1]
Volume Per Day		3,000
Weighted Average Fixed Price		87.00
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Swaps 4
Derivative [Line Items]
Period		2013
Index		Dated Brent
Volume Per Day		3,000
Weighted Average Fixed Price		98.03
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Two Way Collar 1
Derivative [Line Items]
Period		2013
Index		NYMEX WTI	[1]
Volume Per Day		5,000
Weighted Average Fixed Price
Weighted Average Short Put Price
Weighted Average Floor Price		95.00
Weighted Average Ceiling Price		115.00
Crude Oil Commodity Contract | Three Way Collars 3
Derivative [Line Items]
Period		2013
Index		NYMEX WTI	[1]
Volume Per Day		7,000
Weighted Average Fixed Price
Weighted Average Short Put Price		63.57
Weighted Average Floor Price		83.57
Weighted Average Ceiling Price		109.04
Crude Oil Commodity Contract | Three Way Collars 4
Derivative [Line Items]
Period		2013
Index		Dated Brent
Volume Per Day		26,000
Weighted Average Fixed Price
Weighted Average Short Put Price		82.88
Weighted Average Floor Price		100.86
Weighted Average Ceiling Price		127.32
Crude Oil Commodity Contract | Swaps 5
Derivative [Line Items]
Period		2014
Index		NYMEX WTI	[1]
Volume Per Day		11,000
Weighted Average Fixed Price		90.26
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Swaps 6
Derivative [Line Items]
Period		2014
Index		Dated Brent
Volume Per Day		8,000
Weighted Average Fixed Price		105.94
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Crude Oil Commodity Contract | Three Way Collars 6
Derivative [Line Items]
Period		2014
Index		NYMEX WTI
Volume Per Day		4,000
Weighted Average Fixed Price
Weighted Average Short Put Price		77.00
Weighted Average Floor Price		92.00
Weighted Average Ceiling Price		106.13
Crude Oil Commodity Contract | Three Way Collars 5
Derivative [Line Items]
Period		2014
Index		Dated Brent
Volume Per Day		10,000
Weighted Average Fixed Price
Weighted Average Short Put Price		85.00
Weighted Average Floor Price		98.50
Weighted Average Ceiling Price		129.24
Natural Gas Commodity Contract | Swaps 1
Derivative [Line Items]
Period		2012
Index		NYMEX HH (1)	[2]
Volume Per Day		30,000
Weighted Average Fixed Price		5.10
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Natural Gas Commodity Contract | Swaps 2
Derivative [Line Items]
Period		2013
Index		NYMEX HH	[2]
Volume Per Day		30,000
Weighted Average Fixed Price		5.25
Weighted Average Short Put Price
Weighted Average Floor Price
Weighted Average Ceiling Price
Natural Gas Commodity Contract | Three Way Collars 1
Derivative [Line Items]
Period		2012
Index		NYMEX HH	[2]
Volume Per Day		110,000
Weighted Average Fixed Price
Weighted Average Short Put Price		4.44
Weighted Average Floor Price		5.25
Weighted Average Ceiling Price		6.66
Natural Gas Commodity Contract | Three Way Collars 2
Derivative [Line Items]
Period		2013
Index		NYMEX HH	[2]
Volume Per Day		100,000
Weighted Average Fixed Price
Weighted Average Short Put Price		3.88
Weighted Average Floor Price		4.75
Weighted Average Ceiling Price		5.63
Natural Gas Commodity Contract | Two Way Collar 1
Derivative [Line Items]
Period		2012
Index		NYMEX HH	[2]
Volume Per Day		40,000
Weighted Average Fixed Price
Weighted Average Short Put Price
Weighted Average Floor Price		3.25
Weighted Average Ceiling Price		5.14
Natural Gas Commodity Contract | Three Way Collars 3
Derivative [Line Items]
Period		2014
Index		NYMEX HH	[2]
Volume Per Day		55,000
Weighted Average Fixed Price
Weighted Average Short Put Price		2.50
Weighted Average Floor Price		3.50
Weighted Average Ceiling Price		5.25
Natural Gas Commodity Contract | Two Way Collar 2
Derivative [Line Items]
Period		2013
Index		NYMEX HH	[2]
Volume Per Day		40,000
Weighted Average Fixed Price
Weighted Average Short Put Price
Weighted Average Floor Price		3.25
Weighted Average Ceiling Price		5.14
Natural Gas Commodity Contract | Basis Swaps 1
Derivative [Line Items]
Period		2012
Index		IFERC CIG (1)	[3]
Volume Per Day		150,000
Index Less Differential		NYMEX HH
Weighted Average Differential		$ (0.52)

[1] West Texas Intermediate

[2] Henry Hub

[3] Colorado Interstate Gas – Northern System