Derivatives and Risk Management Activities (Details 5) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) contract
Derivatives disclosures
Asset Derivatives Fair Value	$ 244		$ 244		$ 493
Liability Derivatives Fair Value	(127)		(127)		(384)
Broker payable	121		121		133
Initial margin	70		70		126
Variation margin posted/(returned)	(191)		(191)		$ (259)
Net gain/(loss) deferred in AOCI	(208)		(208)
Gain/(loss) expected to be reclassified to earnings through 2018			(16)
Net deferred gain/(loss) recognized in AOCI on derivatives	$ (48)	$ (6)	$ (28)	$ (57)
Number of outstanding derivatives containing credit-risk related contingent features | contract	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	$ 37	2	$ 12	(10)
Interest Rate Derivatives
Derivatives disclosures
Net deferred gain/(loss) recognized in AOCI on derivatives	(85)	$ (8)	(40)	$ (47)
Derivatives designated as hedging instruments
Derivatives disclosures
Asset Derivatives Fair Value	8		8		$ 31
Liability Derivatives Fair Value	(58)		(58)		(83)
Derivatives designated as hedging instruments | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	7		7		23
Liability Derivatives Fair Value	(1)		(1)		(12)
Derivatives designated as hedging instruments | Commodity Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value	1		1		8
Liability Derivatives Fair Value					(1)
Derivatives designated as hedging instruments | Interest Rate Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(19)		(19)		(44)
Derivatives designated as hedging instruments | Interest Rate Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(38)		(38)		(26)
Derivatives not designated as hedging instruments
Derivatives disclosures
Asset Derivatives Fair Value	236		236		462
Liability Derivatives Fair Value	(69)		(69)		(301)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	220		220		439
Liability Derivatives Fair Value	(33)		(33)		(246)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value	16		16		23
Liability Derivatives Fair Value	(5)		(5)		(3)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(19)		(19)		(35)
Derivatives not designated as hedging instruments | Commodity Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(3)		(3)		(5)
Derivatives not designated as hedging instruments | Foreign Currency Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	$ (9)		$ (9)		$ (12)