Percent Of Capital Structure Composed Of Equity

No definition available.

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- Definition

Public Utilities, Requested Rate Increase (Decrease), Amount

+ References

No definition available.

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- Details

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- Definition

Value established for a utility on which the entity is allowed to earn a particular rate of return

+ References

No definition available.

+ Details

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- Definition

The rate of return on common equity that a utility is authorized to recover through regulated rates.

+ References

No definition available.

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- Definition

Revenue Requirement

+ References

No definition available.

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- Definition

Amount of regulatory costs not yet approved by the regulatory authority.

+ References

No definition available.

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- Definition

Carrying amount as of the balance sheet date of investments in power and distribution projects that are expected to be realized after one year or beyond the operating cycle, if longer.

+ 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)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-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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Rate And Regulatory Matters (Narrative-Illinois) (Detail) (USD $)			12 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended						0 Months Ended
	Sep. 30, 2013 Ameren Illinois Company Electric Distribution [Member]	Dec. 31, 2012 Ameren Illinois Company Electric Distribution [Member] Final Rate Order [Member]	Dec. 31, 2012 Ameren Illinois Company Electric Distribution [Member] Rate order appeal [Member]	Sep. 30, 2013 ATXI [Member] Potential Transmission Project Investments Through2019 [Member]	Oct. 11, 2013 Ameren Illinois Company Position [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Jul. 31, 2013 Ameren Illinois Company Position [Member] Ameren Illinois Company Gas Distribution [Member] Pending Rate Case [Member]	Oct. 11, 2013 Icc Staff Recommendation [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Sep. 20, 2013 Icc Staff Recommendation [Member] Ameren Illinois Company Gas Distribution [Member] Pending Rate Case [Member]	Oct. 11, 2013 Increase in recoverable costs [Member] Ameren Illinois Company Position [Member] Ieima [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Oct. 11, 2013 Increase in recoverable costs [Member] Icc Staff Recommendation [Member] Ieima [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Sep. 30, 2013 Revenue Requirement Reconcilation Adjustment [Member] Ameren Illinois Company Electric Distribution [Member]	Dec. 31, 2012 Revenue Requirement Reconcilation Adjustment [Member] Ameren Illinois Company Electric Distribution [Member]	Oct. 11, 2013 Revenue Requirement Reconcilation Adjustment [Member] Ameren Illinois Company Position [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Oct. 11, 2013 Revenue Requirement Reconcilation Adjustment [Member] Icc Staff Recommendation [Member] Ieima [Member] Ameren Illinois Company Electric Distribution [Member] Subsequent Event [Member]	Sep. 30, 2013 Pending Rate Case [Member] Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory Assets	$ 59,000,000
Revenue requirement		765,000,000			798,000,000		789,000,000
Requested rate decrease, amount			11,000,000		(22,000,000)	47,000,000	(42,000,000)	28,000,000	33,000,000	24,000,000			(55,000,000)	(66,000,000)
Rate Of Return On Common Equity						10.40%		8.80%
Percent Of Capital Structure Composed Of Equity						51.80%		50.40%
Rate Base						1,100,000,000		1,100,000,000
Regulatory liability											59,000,000	55,000,000
Amount of Regulatory Costs Not yet Approved															63,000,000
Investments in Power and Distribution Projects				$ 1,100,000,000