Disposal Group, Including Discontinued Operation, Buyer's Indemnification Guarantee Obligation

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- Definition

Disposal Group, Including Discontinued Operation, Buyer's Indemnification Guarantee Obligation, Period

+ References

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- Definition

Disposal Group, Including Discontinued Operation, Obligation to Provide Credit Support, Period

+ References

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- Definition

Related Party Transaction, Guarantees, Maximum Exposure

+ References

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- Definition

Related Party Transaction, Guarantees Outstanding

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- Definition

Related Party Transaction, Purchases of Financing Receivable, Discount

+ References

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- Definition

Amount for accounts payable to related parties.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(k)(1))

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph k

-Subparagraph 1

-Article 4

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

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-Name Accounting Standards Codification

-Topic 944

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-Section S99

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-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 17

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- Definition

The amount of any significant purchases of financing receivables during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (e)

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

-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.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

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-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 16

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph c

-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.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Related Parties

-URI http://asc.fasb.org/extlink&oid=16382449

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-07.1(c))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 07

-Paragraph b

-Subparagraph 1

-Article 6

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Related Party Transactions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			0 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 Ameren Illinois Company [Member]	Jun. 30, 2012 Ameren Illinois Company [Member]	Jun. 30, 2013 Ameren Illinois Company [Member]	Jun. 30, 2012 Ameren Illinois Company [Member]	Jun. 30, 2013 Ameren Missouri [Member]	Jun. 30, 2012 Ameren Missouri [Member]	Jun. 30, 2013 Ameren Missouri [Member]	Jun. 30, 2012 Ameren Missouri [Member]	Jun. 30, 2013 Medina Valley Energy Center [Member]	Jun. 30, 2013 Futures Commission Merchants [Member]	Jun. 30, 2013 Ameren Energy Marketing Company [Member]	Jun. 30, 2013 Ameren Energy Marketing Company [Member] Ameren Illinois Company [Member]	Jun. 30, 2013 Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2012 Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2013 Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2012 Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2013 Related Party One [Member] Ameren Missouri [Member]	Jun. 30, 2012 Related Party One [Member] Ameren Missouri [Member]	Jun. 30, 2013 Related Party One [Member] Ameren Missouri [Member]	Jun. 30, 2012 Related Party One [Member] Ameren Missouri [Member]	Jun. 30, 2013 Guarantee Type, Other [Member]	Mar. 14, 2013 Elgin, Gibson City and Grand Tower Energy Centers [Member] Ameren Energy Generating Company [Member]	Mar. 14, 2013 New Ameren Energy Resources Company, LLC [Member]	Jun. 30, 2013 Miscellaneous Support Services [Member] Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2013 Miscellaneous Support Services [Member] Related Party One [Member] Ameren Illinois Company [Member]	Jun. 30, 2012 Miscellaneous Support Services [Member] Related Party One [Member] Ameren Missouri [Member]	Jun. 30, 2012 Miscellaneous Support Services [Member] Related Party One [Member] Ameren Missouri [Member]
Related Party Transaction [Line Items]
Proceeds from sale of property, plant, and equipment																							$ 100
Accounts payable, related parties													10
Purchase of receivables from Marketing Company													38
Related Party Transaction, Purchases of Financing Receivable, Discount													1
Related Party Transaction, Guarantees Outstanding	230									33	25	166										6
Related Party Transaction, Guarantees, Maximum Exposure												29
Letters of Credit Outstanding, Amount	14
Obligation to provide credit support, period																								24 months
Buyer's indemnification guarantee obligation																								25
Buyer's indemnification guarantee obligation, period																								24 months
Revenue from Related Parties		$ 2.0		$ 2.0			$ 1.0		$ 1.0					$ 7.0	$ 3.0	$ 13.0	$ 5.0	$ 5.0	$ 5.0	$ 12.0	$ 9.0				$ 2.0	$ 2.0	$ 1.0	$ 1.0