Gain on U.S. Department of Energy Settlement (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2009
Gain on U.S. Department of Energy Settlement
Pre-tax gain on U. S. Department of Energy settlement	$ 35.5	$ 35.5
Percent of membership interest in CENG sold (as a percent)			49.99%

Gain or loss on entity's disposition of equity in securities of subsidiaries or 50 percent or less owned persons. Reflects the difference in the parent company's carrying amount of the equity interest in the subsidiary (or equity method investee) immediately before and after all stock transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 13
-Subparagraph g
-Article 9

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration