Derivatives and Risk Management Activities (Details 5) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) contract	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) contract	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) contract
Derivatives disclosures
Asset Derivatives Fair Value	$ 184		$ 184		$ 493
Liability Derivatives Fair Value	(92)		(92)		(384)
Broker payable	46		46		133
Initial margin	49		49		126
Variation margin posted/(returned)	(95)		(95)		$ (259)
Net gain/(loss) deferred in AOCI	(120)		(120)
Net gain/(loss) expected to be reclassified to earnings in next 12 months			4
Gain/(loss) expected to be reclassified to earnings through 2049			(124)
Net deferred gain/(loss) recognized in AOCI on derivatives	$ 92	$ (19)	$ 20	$ (51)
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	$ (28)		$ (25)	(12)
Interest Rate Derivatives
Derivatives disclosures
Net deferred gain/(loss) recognized in AOCI on derivatives	120	$ (19)	45	$ (39)
Derivatives in Hedging Relationships
Derivatives disclosures
Asset Derivatives Fair Value	30		30		$ 31
Liability Derivatives Fair Value	(9)		(9)		(83)
Derivatives in Hedging Relationships | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	11		11		23
Liability Derivatives Fair Value					(12)
Derivatives in Hedging Relationships | Commodity Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value					8
Liability Derivatives Fair Value					(1)
Derivatives in Hedging Relationships | Commodity Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(1)		(1)
Derivatives in Hedging Relationships | Commodity Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Asset Derivatives Fair Value	2		2
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	1		1
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value	16		16
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	(6)		(6)		(44)
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(2)		(2)		(26)
Derivatives Not Designated as a Hedge
Derivatives disclosures
Asset Derivatives Fair Value	154		154		462
Liability Derivatives Fair Value	(83)		(83)		(301)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other current assets
Derivatives disclosures
Asset Derivatives Fair Value	139		139		439
Liability Derivatives Fair Value	(59)		(59)		(246)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other long-term assets, net
Derivatives disclosures
Asset Derivatives Fair Value	14		14		23
Liability Derivatives Fair Value	(1)		(1)		(3)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other current liabilities
Derivatives disclosures
Asset Derivatives Fair Value	1		1
Liability Derivatives Fair Value	(17)		(17)		(35)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other long-term liabilities and deferred credits
Derivatives disclosures
Liability Derivatives Fair Value	(4)		(4)		(5)
Derivatives Not Designated as a Hedge | Foreign Currency Derivatives | Other current liabilities
Derivatives disclosures
Liability Derivatives Fair Value	$ (2)		$ (2)		$ (12)