Derivative and Hedging Activities - Derivative Instruments Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Fair Value	$ (551)	$ (924)
Natural Gas [Member]
Derivative [Line Items]
Volume, Energy Measurement	1,009,000,000,000,000	353,000,000,000,000
Fair Value	(237)	(231)
Natural Gas [Member] | Swap
Derivative [Line Items]
Volume, Energy Measurement	448,000,000,000,000	49,000,000,000,000
Fair Value	(23)	24
Natural Gas [Member] | Call Option
Derivative [Line Items]
Volume, Energy Measurement	193,000,000,000,000	193,000,000,000,000
Fair Value	(210)	(240)
Natural Gas [Member] | Swaptions
Derivative [Line Items]
Volume, Energy Measurement	12,000,000,000,000	0
Fair Value	0	0
Natural Gas [Member] | Basis Swap [Member]
Derivative [Line Items]
Volume, Energy Measurement	68,000,000,000,000	111,000,000,000,000
Fair Value	3	(15)
Natural Gas [Member] | Three Way Collar [Member]
Derivative [Line Items]
Volume, Energy Measurement	288,000,000,000,000	0
Fair Value	(7)	0
Crude Oil [Member]
Derivative [Line Items]
Volume, Volume Measurement	68,200,000	112,700,000
Fair Value	(314)	(693)
Crude Oil [Member] | Swap
Derivative [Line Items]
Volume, Volume Measurement	25,300,000	28,100,000
Fair Value	(50)	68
Crude Oil [Member] | Call Option
Derivative [Line Items]
Volume, Volume Measurement	42,500,000	73,800,000
Fair Value	(265)	(748)
Crude Oil [Member] | Swaptions
Derivative [Line Items]
Volume, Volume Measurement	0	5,300,000
Fair Value	0	(13)
Crude Oil [Member] | Basis Swap [Member]
Derivative [Line Items]
Volume, Volume Measurement	400,000	5,500,000
Fair Value	$ 1	$ 0