Business Description and Significant Accounting Policies Principles of Consolidation (Details) (Intersegment Elimination [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2010	Dec. 31, 2009
Intersegment Elimination [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Overstatement of Utility and Non-regulated revenue and Fuel, purchased power and cost of gas sold in aggregate	$ 59.6	$ 57.5

Amount of each individual error being corrected in the correcting adjustment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 1

-Section N

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 250

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 1.N.Q3)

-URI http://asc.fasb.org/extlink&oid=6369664&loc=d3e30840-122693

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration