Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount (premium).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28567-108399

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

+ Details

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

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://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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

- Definition

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 fourth 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

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Less: Maturities due within one year	$ (580,000,000)		$ (841,000,000)
Long-term Debt, Net	7,859,000,000		7,094,000,000
2022	505,000,000
Thereafter	6,734,000,000
Ameren (parent)
Debt Instrument [Line Items]
Long-term debt, gross	700,000,000		700,000,000
Debt Issuance Costs, Net	(3,000,000)		(4,000,000)
Long-term Debt, Net	697,000,000		696,000,000
Thereafter	350,000,000
Union Electric Company
Debt Instrument [Line Items]
Long-term debt, gross	4,029,000,000		3,988,000,000
Less: Unamortized discount and premium	(9,000,000)		(7,000,000)
Debt Issuance Costs, Net	(22,000,000)		(20,000,000)
Less: Maturities due within one year	(580,000,000)		(384,000,000)
Long-term Debt, Net	3,418,000,000		3,577,000,000
2022	55,000,000
Thereafter	3,054,000,000
Union Electric Company \| City Of Bowling Green Capital Lease Peno Creek Ct
Debt Instrument [Line Items]
Capital Lease Obligations	30,000,000		36,000,000
Union Electric Company \| Audrain County Capital Lease Audrain County Ct
Debt Instrument [Line Items]
Capital Lease Obligations	240,000,000		240,000,000
Ameren Illinois Company
Debt Instrument [Line Items]
Long-term debt, gross	3,330,000,000		2,857,000,000
Less: Unamortized discount and premium	(3,000,000)		(3,000,000)
Debt Issuance Costs, Net	(31,000,000)		(24,000,000)
Less: Maturities due within one year	0		(457,000,000)
Long-term Debt, Net	3,296,000,000		2,373,000,000
2022	400,000,000
Thereafter	2,930,000,000
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Long-term debt, gross	450,000,000		450,000,000
Debt Issuance Costs, Net	(2,000,000)		(2,000,000)
Long-term Debt, Net	448,000,000		448,000,000
2022	50,000,000
Thereafter	400,000,000
Unsecured Debt \| Ameren (parent) \| Senior Unsecured Notes270 due 2020
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000		350,000,000
Long-term debt interest rate	2.70%
Unsecured Debt \| Ameren (parent) \| Senior Unsecured Notes365 due 2026
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000		350,000,000
Long-term debt interest rate	3.65%
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000		450,000,000
Long-term debt interest rate	3.43%
Secured Debt \| Union Electric Company \| 6.40% Senior secured notes due 2017
Debt Instrument [Line Items]
Long-term debt interest rate	6.40%
Secured Debt \| Union Electric Company \| 6.00% Senior secured notes due 2018
Debt Instrument [Line Items]
Debt instrument face amount	$ 0		179,000,000
Long-term debt interest rate	6.00%
Secured Debt \| Union Electric Company \| 5.10% Senior secured notes due 2018
Debt Instrument [Line Items]
Debt instrument face amount	$ 0		199,000,000
Long-term debt interest rate	5.10%
Secured Debt \| Union Electric Company \| 6.70% Senior secured notes due 2019
Debt Instrument [Line Items]
Debt instrument face amount	$ 329,000,000		329,000,000
Long-term debt interest rate	6.70%
Secured Debt \| Union Electric Company \| 5.10% Senior secured notes due 2019
Debt Instrument [Line Items]
Debt instrument face amount	$ 244,000,000		244,000,000
Long-term debt interest rate	5.10%
Secured Debt \| Union Electric Company \| 5.00% Senior secured notes due 2020
Debt Instrument [Line Items]
Debt instrument face amount	$ 85,000,000		85,000,000
Long-term debt interest rate	5.00%
Secured Debt \| Union Electric Company \| Senior Secured Notes350 Due2024
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000		350,000,000
Long-term debt interest rate	3.50%
Secured Debt \| Union Electric Company \| Senior Secured Notes, 2.95%, Due 2027
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000		400,000,000
Long-term debt interest rate	2.95%
Secured Debt \| Union Electric Company \| 5.50% Senior secured notes due 2034
Debt Instrument [Line Items]
Debt instrument face amount	$ 184,000,000		184,000,000
Long-term debt interest rate	5.50%
Secured Debt \| Union Electric Company \| 5.30% Senior secured notes due 2037
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000		300,000,000
Long-term debt interest rate	5.30%
Secured Debt \| Union Electric Company \| 8.45% Senior secured notes due 2039
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000		350,000,000
Long-term debt interest rate	8.45%
Secured Debt \| Union Electric Company \| 3.90% Senior secured notes due 2042
Debt Instrument [Line Items]
Debt instrument face amount	$ 485,000,000		485,000,000
Long-term debt interest rate	3.90%
Secured Debt \| Union Electric Company \| Senior Secured Notes, 3.65%, Due 2045
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000		400,000,000
Long-term debt interest rate	3.65%
Secured Debt \| Union Electric Company \| First Mortgage Bonds, 4.00%, Due 2048 - $425 Issuance [Member]
Debt Instrument [Line Items]
Debt instrument face amount	$ 425,000,000		0
Long-term debt interest rate	4.00%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes6125 Due2017
Debt Instrument [Line Items]
Long-term debt interest rate		6.125%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 6.25% Due 2018
Debt Instrument [Line Items]
Debt instrument face amount	$ 0		144,000,000
Long-term debt interest rate	6.25%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 9.75% Due 2018
Debt Instrument [Line Items]
Debt instrument face amount	$ 0		313,000,000
Long-term debt interest rate	9.75%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes, 2.70%, Due 2022
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000		400,000,000
Long-term debt interest rate	2.70%
Secured Debt \| Ameren Illinois Company \| Series 1993 5.90% Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	$ 1,000,000
Long-term debt interest rate	5.90%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes, 3.25%, Due 2025
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000		300,000,000
Long-term debt interest rate	3.25%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 6.125% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 60,000,000		60,000,000
Long-term debt interest rate	6.125%
Secured Debt \| Ameren Illinois Company \| First Mortgage Bonds, 3.80%, Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	$ 430,000,000		0
Long-term debt interest rate	3.80%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 61,000,000		61,000,000
Long-term debt interest rate	6.70%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 42,000,000		42,000,000
Long-term debt interest rate	6.70%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 4.80% Due 2043
Debt Instrument [Line Items]
Debt instrument face amount	$ 280,000,000		280,000,000
Long-term debt interest rate	4.80%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes 4.30% Due 2044
Debt Instrument [Line Items]
Debt instrument face amount	$ 250,000,000		250,000,000
Long-term debt interest rate	4.30%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes, 4.15%, Due 2046
Debt Instrument [Line Items]
Debt instrument face amount	$ 490,000,000		490,000,000
Long-term debt interest rate	4.15%
Secured Debt \| Ameren Illinois Company \| Senior Secured Notes, 3.70%, Due 2047
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	$ 500,000,000	500,000,000
Long-term debt interest rate	3.70%	3.70%
Secured Debt \| Ameren Illinois Company \| First Mortgage Bonds, 4.50%, Due 2049 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000		0
Long-term debt interest rate	4.50%
Secured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Long-term debt interest rate	3.43%
Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1992 Series due 2022
Debt Instrument [Line Items]
Debt instrument face amount	$ 47,000,000		47,000,000
Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| Series1993 Due2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 1,000,000
Long-term debt interest rate	5.45%
Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series A due 2033
Debt Instrument [Line Items]
Debt instrument face amount	$ 60,000,000		60,000,000
Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series B due 2033
Debt Instrument [Line Items]
Debt instrument face amount	50,000,000		50,000,000
Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series C due 2033
Debt Instrument [Line Items]
Debt instrument face amount	50,000,000		50,000,000
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Illinois Company \| Series 1993 5.90% Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	$ 1,000,000		1,000,000
Long-term debt interest rate	5.90%
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Illinois Company \| Series 1994 A 5.70% Due 2024
Debt Instrument [Line Items]
Debt instrument face amount	$ 1,000,000		1,000,000
Long-term debt interest rate	5.70%
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Illinois Company \| Series B-1 1993 Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 17,000,000		17,000,000
Redemption price, percentage	100.00%
Capital Lease Obligations [Member] \| Union Electric Company
Debt Instrument [Line Items]
Debt Securities, Held-to-maturity	$ 270,000,000		$ 276,000,000
Maximum \| Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000
Maximum \| Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1992 Series due 2022
Debt Instrument [Line Items]
Long-term debt interest rate	18.00%
Maximum \| Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series A due 2033
Debt Instrument [Line Items]
Long-term debt interest rate	18.00%
Maximum \| Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series B due 2033
Debt Instrument [Line Items]
Long-term debt interest rate	18.00%
Maximum \| Environmental Improvement And Pollution Control Revenue Bonds \| Union Electric Company \| 1998 Series C due 2033
Debt Instrument [Line Items]
Long-term debt interest rate	18.00%
Debt Instrument, Redemption, Period One \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
2022	$ 49,500,000
Debt Instrument, Redemption, Period Two \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	49,500,000
Debt Instrument, Redemption, Period Three \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	49,500,000
Debt Instrument, Redemption, Period Four \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	49,500,000
Debt Instrument, Redemption, Period Five \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	49,500,000
Debt Instrument, Redemption, Period Six \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	49,500,000
Debt Instrument, Redemption, Period Seven \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	76,500,000
Debt Instrument, Redemption, Period Eight \| Unsecured Debt \| Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Thereafter	$ 76,500,000