Fair Value Measurement (Unaudited) Unobservable Inputs (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / bbl
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	$ 330
Derivative Asset	116
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	316	[1],[2]
Derivative Asset	101	[1],[2]
Crude Oil Options [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	316
Net realized gains	50	[3]
Net unrealized gains included in earnings related to assets and liabilities still held at the end of the period	36
Net settlement (receipts) payments	301	[4]
Derivative Asset	$ 101
Crude Oil Options [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Assumptions, Implied Volatilities	38.00%
Crude Oil Options [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Assumptions, Implied Volatilities	66.00%
Crude Oil Options [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Deferred Premium Price | $ / bbl	6.89
Crude Oil Options [Member] | Weighted Average [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Assumptions, Implied Volatilities	49.00%
Sales [Member] | Crude Oil Options [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains	$ 51
Interest Expense [Member] | Crude Oil Options [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains	(1)	[3]
Net settlement (receipts) payments	$ 3

[1] Recorded at fair value.

[2] Refer to Note 7 for further discussion and balance sheet classifications. Crude oil options are net of $53 million at September 30, 2015, and $210 million at December 31, 2014, for deferred premiums and accrued interest.

[3] Includes net realized gains of $51 million, partially offset by $1 million of interest expense associated with the deferred premiums.

[4] Includes interest payments of $3 million.