Rate and Regulatory Matters (Regulatory Framework-Illinois) (Details) - Ameren Illinois Company	12 Months Ended
Dec. 31, 2019
FEJA
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage	50.00%
Public Utilities, Approved Return on Equity, Percentage	5.80%
Return on equity adjustment	2.00%
QIP rider
Public Utilities, General Disclosures [Line Items]
QIP recovery begin date	2 months
QIP rider reset	zero
Natural gas
Public Utilities, General Disclosures [Line Items]
Number of months to complete a regulatory rate review	11 months
Electric Distribution \| FEJA
Public Utilities, General Disclosures [Line Items]
Amortization Period	2 years
Maximum \| QIP rider
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage	4.00%
Annual QIP rate cap	5.50%
Maximum \| Electric Distribution \| FEJA
Public Utilities, General Disclosures [Line Items]
Return on equity penalty	0.38%

Amortization period of a regulatory asset or liability

No definition available.

Name:	aee_AmortizationPeriod
Namespace Prefix:	aee_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum annual increase in rates resulting from the QIP rider.

+ References

No definition available.

+ Details

Name:	aee_AnnualQIPratecap
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of months it takes to complete a regulatory rate review.

+ References

No definition available.

+ Details

Name:	aee_Numberofmonthstocompletearegulatoryratereview
Namespace Prefix:	aee_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Recovery of the QIP regulatory asset begins two months after the qualifying natural gas plant is placed in service.

+ References

No definition available.

+ Details

Name:	aee_QIPrecoverybegindate
Namespace Prefix:	aee_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

When QIP rate base is transferred to base rates upon the issuance of a natural gas delivery service rate order, the QIP rider is reset to zero.

+ References

No definition available.

+ Details

Name:	aee_QIPriderreset
Namespace Prefix:	aee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Return on equity adjustment related to the achievement of annual energy efficiency goals.

+ References

No definition available.

+ Details

Name:	aee_Returnonequityadjustment
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Electric distribution return on equity performance standard penalty.

+ References

No definition available.

+ Details

Name:	aee_Returnonequitypenalty
Namespace Prefix:	aee_
Data Type:	num:percentItemType
Balance Type:	na
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

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

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=aee_FEJAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=aee_QIPriderMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilityAxis=srt_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilityAxis=us-gaap_ElectricDistributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: