Fair Value Fair Value of Derivative Contracts (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 341	$ 297
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	109	184
Estimate of Fair Value [Member] | Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	67	80
Derivative Liability	39	68
Estimate of Fair Value [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	274	217
Derivative Liability	70	116
Quoted prices in active markets for identical assets (Level 1) [Member] | Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	4	4
Derivative Liability	7	6
Quoted prices in active markets for identical assets (Level 1) [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	0	0
Derivative Liability	0	0
Significant other observable inputs (Level 2) [Member] | Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	59	46
Derivative Liability	21	31
Significant other observable inputs (Level 2) [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	274	217
Derivative Liability	70	116
Significantunobservable inputs (Level 3) [Member] | Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	4	30
Derivative Liability	11	31
Significantunobservable inputs (Level 3) [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value, derivative	0	0
Derivative Liability	0	0
Energy Related Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	40	36
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(2)	7
Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	230	189
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	26	88
Not Offset on Balance Sheet [Member] | Energy Related Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Asset Adjustment for Financial Instruments subject to Master Netting Agreement but Presented Gross	(27)	(44)
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative, Collateral, Right to Reclaim Cash	14	17
Not Offset on Balance Sheet [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Asset Adjustment for Financial Instruments subject to Master Netting Agreement but Presented Gross	(44)	(28)
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative, Collateral, Right to Reclaim Cash	$ 0	$ 0