Capitalized Exploratory Well Costs (Tables)

12 Months Ended

Dec. 31, 2012

Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]

Capitalized Exploratory Well Costs, Roll Forward [Table Text Block]

	2012			2011			2010
	(in millions)
Balance at January 1,	$	5.0		$	13.6		$	51.7
Additions to capitalized exploratory well costs pending the determination of proved reserves	12.7			—			12.2
Reclassifications to proved properties after the determination of proved reserves	(15.6		)	(8.3		)	(50.3		)
Capitalized exploratory well costs charged to expense	—			(0.3		)	—
Balance at December 31,	$	2.1		$	5.0		$	13.6