Capitalized Exploratory Well Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Capitalized Exploratory Well Costs [Abstract]
Beginning Balance	$ 2.1	$ 5.0	$ 13.6
Additions to capitalized exploratory well costs pending the determination of proved reserves	2.7	12.7	0
Reclassifications to proved properties after the determination of proved reserves	(2.2)	(15.6)	(8.3)
Capitalized exploratory well costs charged to expense	0	0	0
Ending Balance	$ 2.6	$ 2.1	$ 5.0