Energy Supply Agreements Amount

No definition available.

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Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Noncash Or Part Noncash Capital Contribution From Parent

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party Long Term Contract For Purchase Of Electric Power

+ References

No definition available.

+ Details

Name:	aee_RelatedPartyLongTermContractForPurchaseOfElectricPower
Namespace Prefix:	aee_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

- Definition

Related Party, Long Term Contract For Purchase Of Electric Power, Rate

+ References

No definition available.

+ Details

Name:	aee_RelatedPartyLongTermContractForPurchaseOfElectricPowerRate
Namespace Prefix:	aee_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount for accounts payable to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from parent as a source of financing that is recorded as additional paid in capital.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

- 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:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=aee_May312015Member
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=aee_May312017Member
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=aee_IncometaxespayabletoparentMember
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- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=aee_May2014ProcurementMember
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=aee_AmerenIllinoisPowerSupplyAgreementsWithAmerenMissouriMember
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- Details

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- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=aee_September2015ProcurementMember
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- Details

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Related Party Transactions (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) MWh $ / MWh	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Union Electric Company
Related Party Transaction [Line Items]
Accounts payable - affiliates	$ 60	$ 68
Capital contribution from parent	30	44	$ 224
Noncash Or Part Noncash Capital Contribution From Parent	0	0	38
Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts payable - affiliates	70	63
Capital contribution from parent	8	0	$ 25
May 31, 2015 \| Union Electric Company
Related Party Transaction [Line Items]
Energy Supply Agreements Amount	3
May 31, 2017 \| Union Electric Company
Related Party Transaction [Line Items]
Energy Supply Agreements Amount	15
Income taxes payable to parent \| Union Electric Company
Related Party Transaction [Line Items]
Accounts payable - affiliates	11	16
Income taxes payable to parent \| Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts payable - affiliates	$ 17	$ 3
May 2014 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	168,400,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	51,000,000
April 2015 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	667,000,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	36,000,000
September 2015 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	339,000,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	38,000,000
April 2016 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	375,200,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	35,000,000
September 2016 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	82,800,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	34,000,000
April 2017 Procurement [Member] \| Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois Company
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	85,600,000,000
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	34,000,000