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 in Hedging Relationships
Derivatives disclosures
Asset Derivatives Fair Value	8		8		$ 31
Liability Derivatives Fair Value	(58)		(58)		(83)
Derivatives in Hedging Relationships | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	7		7		23
Liability Derivatives Fair Value	(1)		(1)		(12)
Derivatives in Hedging Relationships | Commodity Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value	1		1		8
Liability Derivatives Fair Value					(1)
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(19)		(19)		(44)
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(38)		(38)		(26)
Derivatives Not Designated as a Hedge
Derivatives disclosures
Asset Derivatives Fair Value	236		236		462
Liability Derivatives Fair Value	(69)		(69)		(301)
Derivatives Not Designated as a Hedge | 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 a Hedge | 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 a Hedge | Commodity Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(19)		(19)		(35)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(3)		(3)		(5)
Derivatives Not Designated as a Hedge | Foreign Currency Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	$ (9)		$ (9)		$ (12)