Risk Management and Hedging Activities - Balance Sheet Location (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	$ (197)		$ (133)
Cash collateral receivable (payable), offset against derivative positions	75		12
Derivative Assets (Liabilities), at Fair Value, Net	(122)		(121)
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	41		17
Cash collateral receivable (payable), offset against derivative positions	0		(2)
Derivative Assets (Liabilities), at Fair Value, Net	41		15
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	67		72
Cash collateral receivable (payable), offset against derivative positions	0		0
Derivative Assets (Liabilities), at Fair Value, Net	67		72
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(153)		(71)
Cash collateral receivable (payable), offset against derivative positions	56		1
Derivative Assets (Liabilities), at Fair Value, Net	(97)		(70)
Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(152)		(151)
Cash collateral receivable (payable), offset against derivative positions	19		13
Derivative Assets (Liabilities), at Fair Value, Net	(133)		(138)
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(158)		(121)
Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	40		17
Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	66		66
Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(127)		(61)
Not Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(137)		(143)
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(39)		(12)
Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	1		0
Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	1		6
Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(26)		(10)
Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(15)		(8)
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	135	[1]	98	[1]
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(291)	[1]	(226)	[1]
Derivative, fair value, net	(156)		(128)
Net regulatory asset	223		182		235	400
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	47	[1]	16	[1]
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(11)	[1]	(2)	[1]
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	66	[1]	62	[1]
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0	[1]	(1)	[1]
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	21	[1]	18	[1]
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(146)	[1]	(78)	[1]
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	1	[1]	2	[1]
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(134)	[1]	(145)	[1]
Commodity Contract [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	8		2
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(44)		(14)
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	1		1
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		(1)
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		0
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	5		1
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(27)		(5)
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	2		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(17)		(8)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	4		8
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(6)		(1)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	4		3
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		5
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(2)		(1)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(4)		0
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	1		6
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(4)		(6)
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		0
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	1		6
Derivative liability, fair value, gross liability including not subject to master netting arrangement	0		0
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(4)		(6)
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement	0		0
Derivative liability, fair value, gross liability including not subject to master netting arrangement	$ 0		$ 0

[1] The Company's commodity derivatives not designated as hedging contracts are generally included in regulated rates, and as of December 31, 2014 and 2013, a net regulatory asset of $223 million and $182 million, respectively, was recorded related to the net derivative liability of $156 million and $128 million, respectively.