Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2014

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, 2014 and December 31, 2013:

As of March 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)
Derivative Assets (Liabilities):
Commodity assets	$	—	$	10		$	6		$	16
Commodity liabilities	—		(229		)	(513		)	(742		)
Interest rate liabilities	—		(80		)	—			(80		)
Foreign currency assets	—		7			—			7
Total derivatives	$	—	$	(292	)	$	(507	)	$	(799	)

As of December 31, 2013	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Total Fair Value
			($ in millions)
Derivative Assets (Liabilities):
Commodity assets	$	—	$	25		$	15		$	40
Commodity liabilities	—		(100		)	(493		)	(593		)
Interest rate liabilities	—		(98		)	—			(98		)
Foreign currency assets	—		2			—			2
Total derivatives	$	—	$	(171	)	$	(478	)	$	(649	)

The following table provides fair value measurement information for financial assets (liabilities) measured at fair value on a recurring basis as of March 31, 2014 and December 31, 2013:

As of March 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)
Financial Assets (Liabilities):
Other current assets	$	78		$	—	$	—	$	78
Other current liabilities	(80		)	—		—		(80		)
Total	$	(2	)	$	—	$	—	$	(2	)

As of December 31, 2013	Quoted Prices in Active Markets (Level 1)			Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total Fair Value
				($ in millions)
Financial Assets (Liabilities):
Other current assets	$	80		$	—	$	—	$	80
Other current liabilities	(82		)	—		—		(82		)
Total	$	(2	)	$	—	$	—	$	(2	)