Basis point reduction in FERC allowed base return on common equity

No definition available.

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- Definition

Customer Requested Rate on Equity

+ References

No definition available.

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- Definition

Earnings reduction in FERC allowed base return on common equity

+ References

No definition available.

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- Definition

Incentive adder to FERC allowed base return on common equity

+ References

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Carrying amount as of the balance sheet date of investments in power and distribution projects that are expected to be realized after one year or beyond the operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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- Definition

Cash received for the settlement of litigation during the current period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

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- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

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- 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

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Rate And Regulatory Matters (Narrative-Federal) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2012	Feb. 28, 2015	Nov. 30, 2014	Mar. 31, 2015	Dec. 31, 2014
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				$ 107us-gaap_RegulatoryLiabilityCurrent	106us-gaap_RegulatoryLiabilityCurrent
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				69	84
Ameren Illinois Company \| Pending Ferc Case [Member]
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				8	7
Ameren Illinois Company \| Pending Ferc Case [Member] \| Minimum
Rate And Regulatory Matters [Line Items]
Loss Contingency, Estimate of Possible Loss				8
Ameren Illinois Company \| Pending Ferc Case [Member] \| Maximum
Rate And Regulatory Matters [Line Items]
Loss Contingency, Estimate of Possible Loss				23
Union Electric Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				32	18
Union Electric Company \| New Nuclear Energy Center COL [Member]
Rate And Regulatory Matters [Line Items]
Investments in Power and Distribution Projects				69
Union Electric Company \| New Nuclear Energy Center COL [Member] \| Minimum
Rate And Regulatory Matters [Line Items]
Investments in Power and Distribution Projects				100
Entergy Refund [Member] \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Proceeds from Legal Settlements	31
Midwest Independent Transmission System Operator, Inc [Member] \| Pending Ferc Case [Member]
Rate And Regulatory Matters [Line Items]
Rate Of Return On Common Equity				12.38%
Customer Requested Rate on Equity		8.67%		9.15%
Basis point reduction in FERC allowed base return on common equity				0.50%
Earnings reduction in FERC allowed base return on common equity				4
Incentive adder to FERC allowed base return on common equity			0.50%
Midwest Independent Transmission System Operator, Inc [Member] \| Pending Ferc Case [Member] \| Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Earnings reduction in FERC allowed base return on common equity				$ 2
New England Transmission Owners [Member] \| Pending Ferc Case [Member]
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Return on Equity, Percentage					11.14%
New England Transmission Owners [Member] \| Pending Ferc Case [Member] \| Minimum
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Return on Equity, Percentage					10.57%
New England Transmission Owners [Member] \| Pending Ferc Case [Member] \| Maximum
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Return on Equity, Percentage					11.74%