Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail) gal in Millions, MWh in Millions, MMBTU in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2026 MWh MMBTU gal	Dec. 31, 2025 MWh MMBTU gal
Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	20	25
Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	265	263
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	16	7
Union Electric Company \| Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	20	25
Union Electric Company \| Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	56	46
Union Electric Company \| Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	10	0
Ameren Illinois Company \| Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	0	0
Ameren Illinois Company \| Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	209	217
Ameren Illinois Company \| Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	6	7

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-5A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A

+ Details

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

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-5

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:energyItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-181

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountVolume
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_TradingActivityByTypeAxis=aee_FuelOilsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_TradingActivityByTypeAxis=aee_PowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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