Fair Value Fair Value of Derivative Contracts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	May 01, 2013	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Liability Net, Value	$ (1)	$ 3	$ 18	$ 7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Liability Net, Gain (Loss) Included in Earnings	(4)	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Liability Net, Gain (Loss) Included in Other Comprehensive Income (Loss)	(1)	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Liability Net, Purchases	17	3
Settlements	(16)	(5)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Investment Income	(6)	0
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	80	86
Liability fair value, derivative	(68)	(33)
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	217	603
Liability fair value, derivative	(116)	(1)
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	3
Liability fair value, derivative	(6)	(3)
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
Liability fair value, derivative	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	46	76
Liability fair value, derivative	(31)	(26)
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	217	603
Liability fair value, derivative	(116)	(1)
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	30	7
Liability fair value, derivative	(31)	(4)
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
Liability fair value, derivative	0	0
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	21,128	18,760
Estimate of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 21,550	$ 20,439