Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

The following table provides information for financial assets (liabilities) measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014:

	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Total Fair Value
			($ in millions)
As of March 31, 2015
Derivative Assets (Liabilities):
Commodity assets	$	—	$	579		$	109		$	688
Commodity liabilities	—		(9		)	(178		)	(187		)
Interest rate liabilities	—		(3		)	—			(3		)
Foreign currency liabilities	—		(103		)	—			(103		)
Total derivatives	$	—	$	464		$	(69	)	$	395
As of December 31, 2014
Derivative Assets (Liabilities):
Commodity assets	$	—	$	785		$	205		$	990
Commodity liabilities	—		(9		)	(259		)	(268		)
Interest rate liabilities	—		(17		)	—			(17		)
Foreign currency liabilities	—		(53		)	—			(53		)
Total derivatives	$	—	$	706		$	(54	)	$	652

The following table provides fair value measurement information for the above-noted financial assets (liabilities) measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014:

	Quoted Prices in Active Markets (Level 1)			Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total Fair Value
				($ in millions)
As of March 31, 2015
Financial Assets (Liabilities):
Other current assets	$	60		$	—	$	—	$	60
Other current liabilities	(63		)	—		—		(63		)
Total	$	(3	)	$	—	$	—	$	(3	)
As of December 31, 2014
Financial Assets (Liabilities):
Other current assets	$	57		$	—	$	—	$	57
Other current liabilities	(58		)	—		—		(58		)
Total	$	(1	)	$	—	$	—	$	(1	)