Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less: Maturities due within one year	$ (505,000,000)	$ (8,000,000)
Long-term Debt, Net	12,562,000,000	11,078,000,000
Ameren (parent)
Debt Instrument [Line Items]
Long-term debt, gross	2,550,000,000	1,600,000,000
Less: Unamortized discount and premium	(2,000,000)	(2,000,000)
Debt Issuance Costs, Net	(15,000,000)	(10,000,000)
Long-term Debt, Net	2,533,000,000	1,588,000,000
Union Electric Company
Debt Instrument [Line Items]
Long-term debt, gross	5,669,000,000	5,152,000,000
Less: Unamortized discount and premium	(12,000,000)	(12,000,000)
Debt Issuance Costs, Net	(38,000,000)	(36,000,000)
Less: Maturities due within one year	(55,000,000)	(8,000,000)
Long-term Debt, Net	5,564,000,000	5,096,000,000
Debt Securities, Held-to-maturity	248,000,000	256,000,000
Union Electric Company \| City Of Bowling Green Agreement - Peno Creek Ct
Debt Instrument [Line Items]
Debt instrument face amount	8,000,000	16,000,000
Union Electric Company \| Audrain County Agreement - Audrain County Ct
Debt Instrument [Line Items]
Debt instrument face amount	240,000,000	240,000,000
Ameren Illinois Company
Debt Instrument [Line Items]
Long-term debt, gross	4,438,000,000	3,988,000,000
Less: Unamortized discount and premium	(7,000,000)	(6,000,000)
Debt Issuance Costs, Net	(39,000,000)	(36,000,000)
Less: Maturities due within one year	(400,000,000)	0
Long-term Debt, Net	3,992,000,000	3,946,000,000
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Long-term debt, gross	525,000,000	450,000,000
Debt Issuance Costs, Net	(2,000,000)	(2,000,000)
Less: Maturities due within one year	(50,000,000)	0
Long-term Debt, Net	473,000,000	448,000,000
Unsecured Debt \| Ameren (parent) \| Senior Unsecured Notes 2.50% Due 2024
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	450,000,000
Long-term debt interest rate	2.50%
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 (parent) \| Senior Unsecured Notes 1.95% due 2027
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	0
Long-term debt interest rate	1.95%
Unsecured Debt \| Ameren (parent) \| Senior Secured Notes 1.75% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	0
Long-term debt interest rate	1.75%
Unsecured Debt \| Ameren (parent) \| Senior Secured Notes 3.50% Due 2031
Debt Instrument [Line Items]
Debt instrument face amount	$ 800,000,000	800,000,000
Long-term debt interest rate	3.50%
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 2.45% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 75,000,000	0
Long-term debt interest rate	2.45%
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000.0	450,000,000
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 \| First Mortgage Bonds, 3.50%, Due 2029 - $450 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	450,000,000
Long-term debt interest rate	3.50%
Secured Debt \| Union Electric Company \| First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 465,000,000	465,000,000
Long-term debt interest rate	2.95%
Secured Debt \| Union Electric Company \| Senior Secured Notes 2.15% Due 2032 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	$ 525,000,000	0
Long-term debt interest rate	2.15%
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
Debt Instrument [Line Items]
Debt instrument face amount	$ 425,000,000	425,000,000
Long-term debt interest rate	4.00%
Secured Debt \| Union Electric Company \| First Mortgage Bonds, 3.25%, Due 2049 - $330 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 330,000,000	330,000,000
Long-term debt interest rate	3.25%
Secured Debt \| Union Electric Company \| First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 550,000,000	550,000,000
Long-term debt interest rate	2.625%
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 \| First Mortgage Bonds, 0.375%, $100 Million Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	$ 100,000,000	0
Long-term debt interest rate	0.375%
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
Debt Instrument [Line Items]
Debt instrument face amount	$ 430,000,000	430,000,000
Long-term debt interest rate	3.80%
Secured Debt \| Ameren Illinois Company \| First Mortgage Bonds, 1.55%, Due 2030
Debt Instrument [Line Items]
Debt instrument face amount	$ 375,000,000	375,000,000
Long-term debt interest rate	1.55%
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
Long-term debt interest rate	3.70%
Secured Debt \| Ameren Illinois Company \| First Mortgage Bonds, 4.50%, Due 2049
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	500,000,000
Long-term debt interest rate	4.50%
Secured Debt \| Ameren Illinois Company \| First Mortgage Bonds, 3.25%, Due 2050 - $300
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 \| First Mortgage Bonds, 2.90%, $350 Million Due 2051
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000	0
Long-term debt interest rate	2.90%
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
Long-term debt interest rate	1.60%
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
Long-term debt interest rate	2.90%
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
Long-term debt interest rate	2.90%
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
Long-term debt interest rate	2.75%

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.

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=123466204&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=120400017&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=120391452&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=120398452&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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

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=124435984&loc=d3e28551-108399

Reference 3: 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

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124429444&loc=SL124452920-239629

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

+ 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:	dtr-types: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

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=124435984&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=124435984&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=124435984&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=124435984&loc=d3e28541-108399

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 6: 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

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 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 3: 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=124435984&loc=d3e28555-108399

+ Details

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

- Definition

Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 4: 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=123581744&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 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