Allowed Costs Associated with Debt Redemption

No definition available.

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

- Definition

Disallowed costs associated with debt redemption

+ References

No definition available.

+ Details

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

- Definition

Projected Transmission Project Costs

+ References

No definition available.

+ Details

Name:	aee_ProjectedTransmissionProjectCosts
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Percentage of public utility's approved equity to capital, including debt and equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of public utility's requested equity to capital, including debt and equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedEquityCapitalStructurePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of public utility's requested return on equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

Reference 1: 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_RegulatoryAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

+ Details

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

- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

+ Details

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

- Details

Name:	dei_LegalEntityAxis=aee_AmerenIllinoisCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=aee_AtxiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Rate And Regulatory Matters (Narrative-Illinois) (Details) (USD $)	12 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2014	Jan. 31, 2015	Dec. 09, 2013
Rate And Regulatory Matters [Line Items]
Regulatory assets	$ 1,240,000,000us-gaap_RegulatoryAssetsNoncurrent	$ 1,582,000,000us-gaap_RegulatoryAssetsNoncurrent	$ 1,582,000,000us-gaap_RegulatoryAssetsNoncurrent
Current regulatory assets	156,000,000us-gaap_RegulatoryAssetsCurrent	295,000,000us-gaap_RegulatoryAssetsCurrent	295,000,000us-gaap_RegulatoryAssetsCurrent
Current regulatory liabilities	216,000,000us-gaap_RegulatoryLiabilityCurrent	106,000,000us-gaap_RegulatoryLiabilityCurrent	106,000,000us-gaap_RegulatoryLiabilityCurrent
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory assets	701,000,000	883,000,000	883,000,000
Current regulatory assets	38,000,000	129,000,000	129,000,000
Current regulatory liabilities	159,000,000	84,000,000	84,000,000
Ameren Illinois Company \| Final Rate Order \| Gas Distribution
Rate And Regulatory Matters [Line Items]
Authorized increase in revenue from utility service	32,000,000
Rate base	1,100,000,000
Public Utilities, Approved Return on Equity, Percentage	9.10%
Percent of capital structure composed of equity	51.70%
Ameren Illinois Company \| Final Rate Order \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Disallowed costs associated with debt redemption					15,000,000
Allowed Costs Associated with Debt Redemption		11,000,000
Ameren Illinois Company \| IEMA Revenue Requirement Reconciliation \| IEIMA \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		101,000,000	101,000,000
Current regulatory assets		65,000,000	65,000,000
Current regulatory liabilities	65,000,000
Authorized increase in revenue from utility service		204,000,000
Ameren Illinois Company \| Rate order appeal [Member] \| Gas Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Return on Equity, Percentage	10.40%
ATXI
Rate And Regulatory Matters [Line Items]
Projected Transmission Project Costs			150,000,000
Subsequent Event \| Ameren Illinois Company \| Pending Rate Case [Member] \| Gas Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				53,000,000
Public Utilities, Requested Return on Equity, Percentage				10.25%
Public Utilities, Requested Equity Capital Structure, Percentage				50.00%
Rate base				$ 1,200,000,000