Derivatives and Risk Management Activities (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014 contract	Sep. 30, 2013	Sep. 30, 2014 contract	Sep. 30, 2013	Dec. 31, 2013 contract
Derivatives disclosures
Asset Derivatives Fair Value	$ 83		$ 83		$ 133
Liability Derivatives Fair Value	(77)		(77)		(157)
Net gain/(loss) deferred in AOCI	(118)		(118)
Net gain/(loss) expected to be reclassified to earnings in next 12 months			1
Gain/(loss) expected to be reclassified to earnings through 2045			(119)
Net deferred gain/(loss) recognized in AOCI on derivatives (effective portion)	(6)	78	(57)	141
Broker receivable	35		35		161
Initial margin	74		74		85
Variation margin posted/(returned)			(39)		76
Number of outstanding derivatives containing credit-risk related contingent features	0		0		0
Derivative credit-risk related contingent features			none of our outstanding derivatives contained credit-risk related contingent features that would result in a material adverse impact to us upon any change in our credit ratings
Commodity Derivatives
Derivatives disclosures
Net deferred gain/(loss) recognized in AOCI on derivatives (effective portion)	2	66	(10)	77
Interest Rate Derivatives
Derivatives disclosures
Net deferred gain/(loss) recognized in AOCI on derivatives (effective portion)	(8)	12	(47)	64
Derivatives designated as hedging instruments
Derivatives disclosures
Asset Derivatives Fair Value	11		11		67
Liability Derivatives Fair Value	(15)		(15)		(24)
Derivatives designated as hedging instruments | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	7		7		36
Liability Derivatives Fair Value					(24)
Derivatives designated as hedging instruments | Commodity Derivatives | Other long-term assets
Derivatives disclosures
Asset Derivatives Fair Value	4		4		5
Derivatives designated as hedging instruments | Interest Rate Derivatives | Other long-term assets
Derivatives disclosures
Asset Derivatives Fair Value					26
Derivatives designated as hedging instruments | Interest Rate Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(15)		(15)
Derivatives not designated as hedging instruments
Derivatives disclosures
Asset Derivatives Fair Value	72		72		66
Liability Derivatives Fair Value	(62)		(62)		(133)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	65		65		60
Liability Derivatives Fair Value	(43)		(43)		(117)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other long-term assets
Derivatives disclosures
Asset Derivatives Fair Value	5		5		5
Liability Derivatives Fair Value					(6)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other current liabilities
Derivatives disclosures
Asset Derivatives Fair Value	2		2		1
Liability Derivatives Fair Value	(7)		(7)		(5)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other long-term liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(2)		(2)		(1)
Derivatives not designated as hedging instruments | Foreign Currency Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	$ (10)		$ (10)		$ (4)