Fair Value Measurement (Unaudited) Unobservable Inputs (Details) - Jun. 30, 2015 $ in Millions		USD ($) $ / bbl
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset		$ 330
Derivative Asset		194
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	[1],[2]	316
Derivative Asset	[1],[2]	174
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		21
Net unrealized gains included in earnings related to assets and liabilities still held at the end of the period	[3]	36
Net settlement (receipts) payments	[4]	(199)
Derivative Asset		$ 174
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		28.00%
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		41.00%
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		32.00%
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 unrealized gains included in earnings related to assets and liabilities still held at the end of the period		$ 37
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 unrealized gains included in earnings related to assets and liabilities still held at the end of the period	[3]	1
Net settlement (receipts) payments		$ (2)

[1] Recorded at fair value.

[2] Refer to Note 7 for further discussion and balance sheet classifications. Crude oil options are net of $106 million at June 30, 2015, and $210 million at December 31, 2014, for deferred premiums and accrued interest.

[3] Includes net unrealized gains of $37 million, partially offset by $1 million of interest expense associated with the deferred premiums.

[4] Includes interest payments of $2 million.