Revenue requirement for the electric energy-efficiency investment

No definition available.

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- Definition

Rate And Regulatory Matters [Line Items]

+ References

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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

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Percentage of public utility's requested return on equity.

+ References

No definition available.

+ Details

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- 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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Rate And Regulatory Matters (Narrative-Illinois) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Rate And Regulatory Matters [Line Items]
Regulatory assets		$ 1,205	$ 1,205		$ 1,230
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory assets		822	822		$ 822
Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			17
Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			50
2018 IEIMA Revenue Requirement Reconciliation \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		62	$ 62
Pending Rate Case \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Electric Energy-Efficiency Revenue Requirement		34
Pending Rate Case \| FEJA energy-efficiency rider [Domain] \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 20
Subsequent Event \| Pending Rate Case \| Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 37
Public Utilities, Requested Return on Equity, Percentage	9.87%
Public Utilities, Requested Equity Capital Structure, Percentage				50.00%
Rate Base				$ 1,600
Subsequent Event \| Pending Rate Case \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 72
Subsequent Event \| TCJA - Reduction in Federal Statutory Income Tax Rate \| Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 17