Long-Term Debt and Equity Financings (Schedule of Maturities of Long-Term Debt) (Details) - Ameren Transmission Company of Illinois - Unsecured Debt	Jun. 30, 2017 USD ($)
August 2022
Debt Instrument [Line Items]
Repayments of principal in year five	$ 49,500,000
August 2024
Debt Instrument [Line Items]
Repayments of principal after year five	49,500,000
August 2027
Debt Instrument [Line Items]
Repayments of principal after year five	49,500,000
August 2030
Debt Instrument [Line Items]
Repayments of principal after year five	49,500,000
August 2032
Debt Instrument [Line Items]
Repayments of principal after year five	49,500,000
August 2038
Debt Instrument [Line Items]
Repayments of principal after year five	49,500,000
August 2043
Debt Instrument [Line Items]
Repayments of principal after year five	76,500,000
August 2050
Debt Instrument [Line Items]
Repayments of principal after year five	76,500,000
Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Total principal amount of notes	300,000,000
Senior Unsecured Notes, 3.43%, Due 2050 \| Maximum
Debt Instrument [Line Items]
Total principal amount of notes	$ 450,000,000

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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