Rate And Regulatory Matters [Line Items]

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- Definition

The aggregate revenue, whether regulated or unregulated, derived from the generation, transmission and distribution of electricity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(b))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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- Definition

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

+ References

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- Definition

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

+ References

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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.

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Rate And Regulatory Matters (Narrative-Illinois) (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Rate And Regulatory Matters [Line Items]
Regulatory assets		$ 1,485		$ 1,437
Current regulatory assets		118		149
Electric		1,206	$ 1,102
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory assets		875		816
Current regulatory assets		91		$ 108
Electric		439	392
IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Electric		46	$ 11
2016 IEIMA Revenue Requirement Reconciliation [Member] \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		24
2015 IEIMA Revenue Requirement Reconciliation \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Current regulatory assets		54
2014 IEIMA Revenue Requirement Reconciliation \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Regulatory assets		$ 46
FEJA [Member] \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Equity Capital Structure, Percentage		50.00%
Subsequent Event \| Pending Rate Case \| IEIMA \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 16