Rate And Regulatory Matters [Line Items]

No definition available.

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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.

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- Definition

Refunds to customers as a result of the reduction in the federal corporate income tax rate as a result of the Tax Cuts and Jobs Act.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Percentage of public utility's requested return on equity.

+ References

No definition available.

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- 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

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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

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Rate And Regulatory Matters (Narrative-Illinois) (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Rate And Regulatory Matters [Line Items]
Regulatory assets		$ 1,205	$ 1,230
Current regulatory assets		130	144
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory assets		812	822
Current regulatory assets		69	$ 87
Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Tax Reform Refunds From the Tax Cuts and Jobs Act		16
Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Tax Reform Refunds From the Tax Cuts and Jobs Act		50
2017 IEIMA Revenue Requirement Reconciliation [Member] \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		52
2016 IEIMA Revenue Requirement Reconciliation \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Current regulatory assets		19
2018 IEIMA Revenue Requirement Reconciliation \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		42
Pending Rate Case \| Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 49
Public Utilities, Requested Equity Capital Structure, Percentage		50.00%
Rate Base		$ 1,600
Components of Rate Increase \| Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 42
Subsequent Event \| Pending Rate Case \| Ameren Illinois Company \| Natural Gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 44
Public Utilities, Requested Return on Equity, Percentage	9.87%
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