Annual coal reserve payments to be made by Company.

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Company's Share Of Construction Costs.

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- Definition

First coal reserve payment made by the Company.

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- Definition

Number of tons of coal in which the Company was named the winning bidder.

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- Definition

Undivided interest percent of new electricity generation project.

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- Definition

Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 17

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

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The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid within one year of the balance sheet date.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 7

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)

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The amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation as of the balance sheet date.

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Commitments and Contingencies (Details 1) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Jul. 31, 2011 T	Sep. 30, 2011 Prarie State Energy Campus Member [Member]	Dec. 31, 2010 Prarie State Energy Campus Member [Member]	Sep. 30, 2011 Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Expenditures for construction of Prairie State Energy Campus	$ 29.8	$ 52.5		$ 29.8
Commitments outstanding for capital expenditures, Current						521.4
Investment in Prairie State Energy Campus included in Investments and Other Assets				232.3	202.5
Company's estimated share of total construction costs				250
Number of tons of coal in the Powder River Basin of Wyoming in which the Company was named the winning bidder			220,000,000
Commitments outstanding for capital expenditures next year						477.6
Subsidiary Company's Interest in Prairie State Energy Campus	5.06%			5.06%
First coal reserve payment made by the Company			42.1
Annual coal reserve payments to be made by the Company in July of each of the next four years			$ 42.1