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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-4

+ 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/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

+ 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

+ 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-8A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 10: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 12: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 30: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 31: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

+ 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://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-1A

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

+ 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, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as current. Excludes lease obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(20))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ 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 requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 10
-Topic 470
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481544/470-10-50-1

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

+ Details

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

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ 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 ($) $ in Millions	Feb. 01, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Apr. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Oct. 31, 2024	Aug. 31, 2024	Jun. 30, 2024	Jan. 31, 2024
Debt Instrument [Line Items]
Less: Maturities due within one year		$ (973)					$ (317)
Long-Term Debt, Excluding Current Maturities		18,214					17,262
Thereafter		14,394
Ameren (parent)
Debt Instrument [Line Items]
Total long-term debt, gross		4,150					3,400
Less: Unamortized discount and premium		(3)					(3)
Less: Unamortized debt issuance costs		(16)					(14)
Long-Term Debt, Excluding Current Maturities		3,181					3,383
Thereafter		1,550
Ameren Missouri
Debt Instrument [Line Items]
Total long-term debt, gross		8,308					7,825
Less: Unamortized discount and premium		(15)					(17)
Less: Unamortized debt issuance costs		(62)					(62)
Less: Maturities due within one year		(23)					(17)
Long-Term Debt, Excluding Current Maturities		8,120					7,671
Thereafter		6,864
Ameren Missouri \| Related Party
Debt Instrument [Line Items]
Less: Unamortized debt issuance costs		(1)					(1)
Long-Term Debt, Excluding Current Maturities		87					57
Ameren Illinois
Debt Instrument [Line Items]
Total long-term debt, gross		6,313					5,913
Less: Unamortized discount and premium		2					(10)
Less: Unamortized debt issuance costs		(56)					(51)
Less: Maturities due within one year		0					(300)
Long-Term Debt, Excluding Current Maturities		6,254					5,549
Thereafter		5,448
Ameren Illinois \| Related Party
Debt Instrument [Line Items]
Long-Term Debt, Excluding Current Maturities		5					3
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Total long-term debt, gross		661					661
Less: Unamortized debt issuance costs		(2)					(2)
Long-Term Debt, Excluding Current Maturities		659					659
Thereafter		$ 532
Unsecured Debt \| Ameren (parent) \| 3.65% Senior unsecured notes due 2026
Debt Instrument [Line Items]
Long-term debt interest rate		3.65%
Debt instrument face amount		$ (350)					(350)
Unsecured Debt \| Ameren (parent) \| 5.70% Senior unsecured notes due 2026
Debt Instrument [Line Items]
Long-term debt interest rate		5.70%
Debt instrument face amount		$ (600)					(600)
Unsecured Debt \| Ameren (parent) \| 1.95% Senior unsecured notes due 2027
Debt Instrument [Line Items]
Long-term debt interest rate		1.95%
Debt instrument face amount		$ (500)					(500)
Unsecured Debt \| Ameren (parent) \| 1.75% Senior unsecured notes due 2028
Debt Instrument [Line Items]
Long-term debt interest rate		1.75%
Debt instrument face amount		$ (450)					(450)
Unsecured Debt \| Ameren (parent) \| 5.00% Senior unsecured notes due 2029
Debt Instrument [Line Items]
Long-term debt interest rate		5.00%
Debt instrument face amount		$ (700)					(700)
Unsecured Debt \| Ameren (parent) \| 3.50% Senior unsecured notes due 2031
Debt Instrument [Line Items]
Long-term debt interest rate		3.50%
Debt instrument face amount		$ (800)					(800)
Unsecured Debt \| Ameren (parent) \| Senior Unsecured Notes, 5.375%, Due 2035
Debt Instrument [Line Items]
Long-term debt interest rate		5.375%
Debt instrument face amount		$ (750)					0
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036
Debt Instrument [Line Items]
Long-term debt interest rate		2.45%
Debt instrument face amount		$ (75)					(75)
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036 \| Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Thereafter		30
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036 \| Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Thereafter		$ 45
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 5.17%, Due 2039
Debt Instrument [Line Items]
Long-term debt interest rate		5.17%							5.17%
Debt instrument face amount		$ (70)					(70)		$ (70)
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050
Debt Instrument [Line Items]
Long-term debt interest rate		3.43%							3.43%
Debt instrument face amount		$ (351)					(351)
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.96% Senior unsecured notes due 2052
Debt Instrument [Line Items]
Long-term debt interest rate		2.96%
Debt instrument face amount		$ (95)					(95)
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.96% Senior unsecured notes due 2052 \| Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Thereafter		45
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.96% Senior unsecured notes due 2052 \| Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Thereafter		$ 50
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 5.42%, Due 2053
Debt Instrument [Line Items]
Long-term debt interest rate		5.42%							5.42%
Debt instrument face amount		$ (70)					(70)		$ (70)
Secured Debt \| Ameren Missouri \| Related Party
Debt Instrument [Line Items]
Debt instrument face amount		$ (88)					(58)
Secured Debt \| Ameren Missouri \| 3.65% Senior unsecured notes due 2026 \| Subsequent Event
Debt Instrument [Line Items]
Long-term debt interest rate	3.65%
Debt instrument face amount	$ (350)
Secured Debt \| Ameren Missouri \| Senior Unsecured Notes, 5.375%, Due 2035
Debt Instrument [Line Items]
Long-term debt interest rate						5.375%
Debt instrument face amount						$ (750)
Secured Debt \| Ameren Missouri \| 2.95% senior secured notes due 2027
Debt Instrument [Line Items]
Long-term debt interest rate		2.95%
Debt instrument face amount		$ (400)					(400)
Secured Debt \| Ameren Missouri \| 3.50% First mortgage bonds due 2029
Debt Instrument [Line Items]
Long-term debt interest rate		3.50%
Debt instrument face amount		$ (450)					(450)
Secured Debt \| Ameren Missouri \| 2.95% First mortgage bonds due 2030
Debt Instrument [Line Items]
Long-term debt interest rate		2.95%
Debt instrument face amount		$ (465)					(465)
Secured Debt \| Ameren Missouri \| 2.15% First mortgage bonds due 2032
Debt Instrument [Line Items]
Long-term debt interest rate		2.15%
Debt instrument face amount		$ (525)					(525)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds 5.20% Due 2034
Debt Instrument [Line Items]
Long-term debt interest rate		5.20%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Missouri \| 5.50% Senior secured notes due 2034
Debt Instrument [Line Items]
Long-term debt interest rate		5.50%
Debt instrument face amount		$ (184)					(184)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds, 5.25%, Due 2035
Debt Instrument [Line Items]
Long-term debt interest rate		5.25%			5.25%
Debt instrument face amount		$ (500)			$ (500)		0
Secured Debt \| Ameren Missouri \| 5.30% Senior secured notes due 2037
Debt Instrument [Line Items]
Long-term debt interest rate		5.30%
Debt instrument face amount		$ (300)					(300)
Secured Debt \| Ameren Missouri \| 8.45% Senior secured notes due 2039
Debt Instrument [Line Items]
Long-term debt interest rate		8.45%
Debt instrument face amount		$ (350)					$ (350)
Secured Debt \| Ameren Missouri \| 4.85% Securitized Utility Tariff Bonds Due 2039
Debt Instrument [Line Items]
Long-term debt interest rate		4.85%					4.85%
Debt instrument face amount		$ (459)					$ (476)
Secured Debt \| Ameren Missouri \| 3.90% Senior secured notes due 2042
Debt Instrument [Line Items]
Long-term debt interest rate		3.90%
Debt instrument face amount		$ (485)					(485)
Secured Debt \| Ameren Missouri \| 3.65% Senior secured notes due 2045
Debt Instrument [Line Items]
Long-term debt interest rate		3.65%
Debt instrument face amount		$ (400)					(400)
Secured Debt \| Ameren Missouri \| 3.65% Senior secured notes due 2045 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		3.65%
Debt instrument face amount		$ (29)					(7)
Secured Debt \| Ameren Missouri \| 4.00% First mortgage bonds due 2048
Debt Instrument [Line Items]
Long-term debt interest rate		4.00%
Debt instrument face amount		$ (425)					(425)
Secured Debt \| Ameren Missouri \| 4.00% First mortgage bonds due 2048 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		4.00%
Debt instrument face amount		$ (4)					0
Secured Debt \| Ameren Missouri \| 3.25% First Mortgage bonds due 2049
Debt Instrument [Line Items]
Long-term debt interest rate		3.25%
Debt instrument face amount		$ (330)					(330)
Secured Debt \| Ameren Missouri \| 3.25% First Mortgage bonds due 2049 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		3.25%
Debt instrument face amount		$ (33)					(33)
Secured Debt \| Ameren Missouri \| 2.625% First Mortgage bonds due 2051
Debt Instrument [Line Items]
Long-term debt interest rate		2.625%
Debt instrument face amount		$ (550)					(550)
Secured Debt \| Ameren Missouri \| 2.625% First Mortgage bonds due 2051 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		2.625%
Debt instrument face amount		$ (7)					(4)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance
Debt Instrument [Line Items]
Long-term debt interest rate		3.90%
Debt instrument face amount		$ (525)					(525)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		3.90%
Debt instrument face amount		$ (15)					(14)
Secured Debt \| Ameren Missouri \| 5.45% First mortgage bonds due 2053
Debt Instrument [Line Items]
Long-term debt interest rate		5.45%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance
Debt Instrument [Line Items]
Long-term debt interest rate		5.25%									5.25%
Debt instrument face amount		$ (350)					(350)				$ (350)
Secured Debt \| Ameren Missouri \| First Mortgage Bonds, 5.125%, Due 2055 - $450 Issuance
Debt Instrument [Line Items]
Long-term debt interest rate		5.125%						5.125%
Debt instrument face amount		$ (450)					(450)	$ (450)
Secured Debt \| Ameren Illinois \| Related Party
Debt Instrument [Line Items]
Debt instrument face amount		$ (5)					(3)
Secured Debt \| Ameren Illinois \| 3.25% First Mortgage bonds due 2025
Debt Instrument [Line Items]
Long-term debt interest rate		3.25%
Debt instrument face amount		$ 0					(300)
Secured Debt \| Ameren Illinois \| 6.125% First Mortgage bonds due 2028
Debt Instrument [Line Items]
Long-term debt interest rate		6.125%
Debt instrument face amount		$ (60)					(60)
Secured Debt \| Ameren Illinois \| 3.80% First Mortgage bonds due 2028
Debt Instrument [Line Items]
Long-term debt interest rate		3.80%
Debt instrument face amount		$ (430)					(430)
Secured Debt \| Ameren Illinois \| 1.55% First Mortgage bonds due 2030
Debt Instrument [Line Items]
Long-term debt interest rate		1.55%
Debt instrument face amount		$ (375)					(375)
Secured Debt \| Ameren Illinois \| 3.85% First mortgage bonds due 2032
Debt Instrument [Line Items]
Long-term debt interest rate		3.85%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Illinois \| 4.95% First mortgage bonds due 2033
Debt Instrument [Line Items]
Long-term debt interest rate		4.95%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Illinois \| 6.70% First Mortgage bonds due 2036
Debt Instrument [Line Items]
Long-term debt interest rate		6.70%
Debt instrument face amount		$ (61)					(61)
Secured Debt \| Ameren Illinois \| 6.70% First Mortgage bonds due 2036
Debt Instrument [Line Items]
Long-term debt interest rate		6.70%
Debt instrument face amount		$ (42)					(42)
Secured Debt \| Ameren Illinois \| 4.80% First Mortgage bonds due 2043
Debt Instrument [Line Items]
Long-term debt interest rate		4.80%
Debt instrument face amount		$ (280)					(280)
Secured Debt \| Ameren Illinois \| 4.30% First Mortgage bonds due 2044
Debt Instrument [Line Items]
Long-term debt interest rate		4.30%
Debt instrument face amount		$ (250)					(250)
Secured Debt \| Ameren Illinois \| 4.15% First Mortgage bonds due 2046
Debt Instrument [Line Items]
Long-term debt interest rate		4.15%
Debt instrument face amount		$ (490)					(490)
Secured Debt \| Ameren Illinois \| 3.70% First Mortgage bonds due 2047
Debt Instrument [Line Items]
Long-term debt interest rate		3.70%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Illinois \| 3.70% First Mortgage bonds due 2047 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		3.70%
Debt instrument face amount		$ (1)					(1)
Secured Debt \| Ameren Illinois \| 4.50% First Mortgage bonds due 2049
Debt Instrument [Line Items]
Long-term debt interest rate		4.50%
Debt instrument face amount		$ (500)					(500)
Secured Debt \| Ameren Illinois \| 3.25% First Mortgage bonds due 2050
Debt Instrument [Line Items]
Long-term debt interest rate		3.25%
Debt instrument face amount		$ (300)					(300)
Secured Debt \| Ameren Illinois \| 3.25% First Mortgage bonds due 2050 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		3.25%
Debt instrument face amount		$ (2)					(2)
Secured Debt \| Ameren Illinois \| 2.90% First Mortgage bonds due 2051
Debt Instrument [Line Items]
Long-term debt interest rate		2.90%
Debt instrument face amount		$ (350)					(350)
Secured Debt \| Ameren Illinois \| 2.90% First Mortgage bonds due 2051 \| Related Party
Debt Instrument [Line Items]
Long-term debt interest rate		2.90%
Debt instrument face amount		$ (2)					0
Secured Debt \| Ameren Illinois \| 5.90% First mortgage bonds due 2052
Debt Instrument [Line Items]
Long-term debt interest rate		5.90%
Debt instrument face amount		$ (350)					(350)
Secured Debt \| Ameren Illinois \| 5.55% First mortgage bonds due 2054
Debt Instrument [Line Items]
Long-term debt interest rate		5.55%								5.55%
Debt instrument face amount		$ (625)					(625)			$ (625)
Secured Debt \| Ameren Illinois \| First Mortgage Bonds, 5.625%, Due 2055
Debt Instrument [Line Items]
Long-term debt interest rate		5.625%	5.625%			5.625%
Debt instrument face amount		$ (700)		$ (350)		$ (350)	0
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Missouri \| 2.90% 1998 Series A due 2033
Debt Instrument [Line Items]
Long-term debt interest rate		2.90%
Debt instrument face amount		$ (60)					(60)
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Missouri \| 2.90% 1998 Series B due 2033
Debt Instrument [Line Items]
Long-term debt interest rate		2.90%
Debt instrument face amount		$ (50)					(50)
Environmental Improvement And Pollution Control Revenue Bonds \| Ameren Missouri \| 2.75% 1998 Series C due 2033
Debt Instrument [Line Items]
Long-term debt interest rate		2.75%
Debt instrument face amount		$ (50)					$ (50)