Percentage of Fixed non-volumetric customer charge

No definition available.

Name:	aee_PercentageOfFixedNonVolumetricCustomerCharge
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent Of Capital Structure Composed Of Equity

+ References

No definition available.

+ Details

Name:	aee_PercentOfCapitalStructureComposedOfEquity
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Public Utilities, Requested Rate Increase (Decrease), Amount

+ References

No definition available.

+ Details

Name:	aee_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	aee_RateAndRegulatoryMattersLineItems
Namespace Prefix:	aee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	aee_RateBase
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	aee_RateOfReturnOnCommonEquity
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue Requirement

+ References

No definition available.

+ Details

Name:	aee_RevenueRequirement
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

+ Details

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_RegulatoryLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Rate And Regulatory Matters (Narrative-Illinois) (Detail) (Ameren Illinois Company [Member], USD $)			12 Months Ended	0 Months Ended		1 Months Ended	0 Months Ended		0 Months Ended					0 Months Ended		1 Months Ended
	Jun. 30, 2013 Electric Distribution [Member]	Dec. 31, 2012 Electric Distribution [Member] Final Rate Order [Member]	Dec. 31, 2012 Electric Distribution [Member] Rate order appeal [Member]	Jul. 30, 2013 Ameren Illinois Company Position [Member] Electric Distribution [Member]	Jul. 31, 2013 Ameren Illinois Company Position [Member] Electric Distribution [Member]	Jul. 31, 2013 Ameren Illinois Company Position [Member] Gas Distribution [Member] Pending Rate Case [Member]	Jul. 02, 2013 Icc Staff Recommendation [Member] Electric Distribution [Member]	Jul. 31, 2013 Icc Staff Recommendation [Member] Electric Distribution [Member]	Aug. 08, 2013 Icc Staff Recommendation [Member] Gas Distribution [Member] Pending Rate Case [Member]	Jul. 30, 2013 Increase in recoverable costs [Member] Ameren Illinois Company Position [Member] Ieima [Member] Electric Distribution [Member]	Jul. 02, 2013 Increase in recoverable costs [Member] Icc Staff Recommendation [Member] Ieima [Member] Electric Distribution [Member]	Jun. 30, 2013 Revenue Requirement Reconcilation Adjustment [Member] Electric Distribution [Member]	Dec. 31, 2012 Revenue Requirement Reconcilation Adjustment [Member] Electric Distribution [Member]	Jul. 30, 2013 Revenue Requirement Reconcilation Adjustment [Member] Ameren Illinois Company Position [Member] Electric Distribution [Member]	Jul. 02, 2013 Revenue Requirement Reconcilation Adjustment [Member] Icc Staff Recommendation [Member] Ieima [Member] Electric Distribution [Member]	Jan. 31, 2013 Minimum [Member] Gas Distribution [Member] Pending Rate Case [Member]	Jan. 31, 2013 Maximum [Member] Gas Distribution [Member] Pending Rate Case [Member]
Rate And Regulatory Matters [Line Items]
Regulatory Assets	$ 33,000,000
Revenue requirement		765,000,000			783,000,000			772,000,000
Requested rate decrease, amount			11,000,000	(38,000,000)		50,000,000	(60,000,000)		24,000,000	18,000,000	8,000,000			(56,000,000)	(68,000,000)
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												$ 57,000,000	$ 55,000,000
Percentage of Fixed non-volumetric customer charge																80.00%	85.00%