Gain (Loss) On Disposition Of Assets, Net (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Gain (loss) on disposition of assets in continuing operations	$ 43.6	$ 2.2
Eagle Ford Shale [Member]
Segment Reporting Information [Line Items]
Sale of interest in an unproved oil and gas property	55.2
Gain (loss) on disposition of assets in continuing operations	$ 43.1