Commitments and Contingencies (Pumped-Storage Hydroelectric Facility Breach) (Details) (USD $) In Millions	79 Months Ended
Jun. 30, 2011	Sep. 30, 2011
Commitments and Contingencies
Payments relating to Taum Sauk incident damage and cleanup	$ 208
Payments relating to Taum Sauk incident damage and cleanup recorded to expense and not covered by insurance	36
Cumulative payments relating to Taum Sauk incident damage and cleanup covered by insurance and recorded as a receivable	172
Cumulative liability insurance reimbursements received for Taum Sauk incident	104
Insurance settlements receivable	68
Disallowed capitalized costs associated with rebuilt Taum Sauk energy center		$ 89

Cumulative payments relating to Taum Sauk incident damage and cleanup covered by insurance and recorded as a receivable.

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Payments relating to Taum Sauk incident damage and cleanup.

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Payments relating to Taum Sauk incident damage and cleanup recorded to expense and not covered by insurance.

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- Definition

The amount recovered from insurance. These recoveries reduce costs and losses that are reported as a separate line item under operating expenses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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Amount due in settlement of a claim for reimbursement from an insurance company when the Company has suffered a loss covered under an insurance policy.

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- Definition

The amount of disallowed costs for rate making purposes for recently completed plants in regulated industries when this becomes probable. Such charges do not meet the requirements of an extraordinary item.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 10.E)
-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e660019-123033

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 90
-Paragraph 7
-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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 10
-Section E

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section 35
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6500292&loc=d3e45799-110387

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