Derivative and Hedging Activities - Netting Offsets Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term derivative assets	$ 0	$ 58
Long-term derivative assets	4	2
Short-term derivative liabilities	(208)	(105)
Long-term derivative liabilities	(445)	(934)
Commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	40	115
Derivative Liability	593	1,039
Short [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term derivative liabilities	208
Short [Member] | Commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	29	110
Derivative Asset, Fair Value, Amount Offset Against Collateral	(29)	(52)
Derivative Asset	0	58
Liability commodity contracts	(231)	(157)
Derivative Liability, Fair Value, Amount Offset Against Collateral	29	52
Derivative Liability	(202)	(105)
Short-term derivative assets		58
Short-term derivative liabilities		105
Short [Member] | Interest rate contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset	0	0
Liability commodity contracts	(6)	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability	(6)	0
Short [Member] | Foreign currency contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset	0	0
Liability commodity contracts	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability	0	0
Long [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term derivative assets	4
Long [Member] | Commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	11	5
Derivative Asset, Fair Value, Amount Offset Against Collateral	(9)	(3)
Derivative Asset	2	2
Liability commodity contracts	(362)	(882)
Derivative Liability, Fair Value, Amount Offset Against Collateral	9	3
Derivative Liability	(353)	(879)
Long-term derivative assets		2
Long-term derivative liabilities		934
Long [Member] | Interest rate contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset	0	0
Liability commodity contracts	(92)	(35)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability	(92)	(35)
Long [Member] | Foreign currency contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset commodity contracts	2	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset	2	0
Liability commodity contracts	0	(20)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability	$ 0	$ (20)