Income Taxes Income Taxes (Narrative) (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Income Taxes [Line Items]
Adjustment of deferred tax (asset) liability	$ 13	$ 13
Union Electric Company
Income Taxes [Line Items]
Adjustment of deferred tax (asset) liability	4	4
Ameren Illinois Company
Income Taxes [Line Items]
Adjustment of deferred tax (asset) liability	4	$ 4
State and Local Jurisdiction \| Union Electric Company
Income Taxes [Line Items]
State Income Tax Statutory Rate		4.00%
Deferred tax liabilities, net	$ 33	$ 33
State and Local Jurisdiction \| Maximum \| Union Electric Company
Income Taxes [Line Items]
State Income Tax Statutory Rate		6.25%

[Line Items] for Income Taxes [Table]

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The statutory income tax rate applied to taxable income within a state's jurisdiction.

+ References

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- Definition

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31931-109318

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

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