Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($)	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Regulatory assets:
Less: current regulatory assets	$ (387,000,000)	$ (366,000,000)
Noncurrent regulatory assets	2,524,000,000	2,397,000,000
Regulatory liabilities:
Noncurrent regulatory liabilities	6,255,000,000	5,897,000,000
Ameren Missouri
Regulatory assets:
Total regulatory assets	1,631,000,000	1,432,000,000
Less: current regulatory assets	(181,000,000)	(66,000,000)
Noncurrent regulatory assets	1,450,000,000	1,366,000,000
Regulatory liabilities:
Total regulatory liabilities	3,347,000,000	3,213,000,000
Less: current regulatory liabilities	(23,000,000)	(37,000,000)
Noncurrent regulatory liabilities	$ 3,324,000,000	$ 3,176,000,000
PISA deferral percentage	85.00%
Ameren Missouri \| Rush Island Energy Center
Regulatory liabilities:
Regulatory asset, amortization period		15 years
Amortization of regulatory asset		$ 15
Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 1,248,000,000	1,292,000,000
Less: current regulatory assets	(189,000,000)	(281,000,000)
Noncurrent regulatory assets	1,059,000,000	1,011,000,000
Regulatory liabilities:
Total regulatory liabilities	2,907,000,000	2,652,000,000
Less: current regulatory liabilities	(132,000,000)	(79,000,000)
Noncurrent regulatory liabilities	2,775,000,000	2,573,000,000
Ameren (parent)
Regulatory assets:
Total regulatory assets	2,911,000,000	2,763,000,000
Less: current regulatory assets	(387,000,000)	(366,000,000)
Noncurrent regulatory assets	2,524,000,000	2,397,000,000
Regulatory liabilities:
Total regulatory liabilities	6,413,000,000	6,017,000,000
Less: current regulatory liabilities	(158,000,000)	(120,000,000)
Noncurrent regulatory liabilities	6,255,000,000	5,897,000,000
Under-recovered FAC
Regulatory assets:
Total regulatory assets	137,000,000	41,000,000
Under-recovered FAC \| Ameren Missouri
Regulatory assets:
Total regulatory assets	137,000,000	41,000,000
Under-recovered FAC \| Ameren Illinois
Regulatory assets:
Total regulatory assets	0	0
MTM derivative losses
Regulatory assets:
Total regulatory assets	126,000,000	103,000,000
MTM derivative losses \| Ameren Missouri
Regulatory assets:
Total regulatory assets	15,000,000	15,000,000
MTM derivative losses \| Ameren Illinois
Regulatory assets:
Total regulatory assets	111,000,000	88,000,000
IEIMA revenue requirement reconciliation adjustment
Regulatory assets:
Total regulatory assets	0	139,000,000
IEIMA revenue requirement reconciliation adjustment \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
IEIMA revenue requirement reconciliation adjustment \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 0	139,000,000
Regulatory liabilities:
Regulatory asset, amortization period	2 years
MYRP revenue requirement reconciliation adjustment
Regulatory assets:
Total regulatory assets	$ 74,000,000	24,000,000
MYRP revenue requirement reconciliation adjustment \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
MYRP revenue requirement reconciliation adjustment \| Ameren Illinois
Regulatory assets:
Total regulatory assets	74,000,000	24,000,000
Under-recovered RBA
Regulatory assets:
Total regulatory assets	29,000,000	22,000,000
Under-recovered RBA \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Under-recovered RBA \| Ameren Illinois
Regulatory assets:
Total regulatory assets	29,000,000	22,000,000
FERC revenue requirement reconciliation adjustment
Regulatory assets:
Total regulatory assets	$ 73,000,000	90,000,000
Regulatory liabilities:
Regulatory asset, amortization period	2 years
FERC revenue requirement reconciliation adjustment \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 0	0
FERC revenue requirement reconciliation adjustment \| Ameren Illinois
Regulatory assets:
Total regulatory assets	45,000,000	55,000,000
Under-recovered VBA
Regulatory assets:
Total regulatory assets	21,000,000	49,000,000
Under-recovered VBA \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Under-recovered VBA \| Ameren Illinois
Regulatory assets:
Total regulatory assets	21,000,000	49,000,000
Income taxes
Regulatory assets:
Total regulatory assets	376,000,000	322,000,000
Regulatory liabilities:
Total regulatory liabilities	$ 1,587,000,000	1,804,000,000
Weighted-average amortization period	38 years
Income taxes \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 282,000,000	237,000,000
Regulatory liabilities:
Total regulatory liabilities	$ 963,000,000	1,040,000,000
Regulatory asset, amortization period	5 years
Weighted-average amortization period	30 years
Income taxes \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 91,000,000	81,000,000
Regulatory liabilities:
Total regulatory liabilities	$ 546,000,000	679,000,000
Weighted-average amortization period	44 years
Bad debt rider
Regulatory assets:
Total regulatory assets	$ 13,000,000	25,000,000
Bad debt rider \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Bad debt rider \| Ameren Illinois
Regulatory assets:
Total regulatory assets	13,000,000	25,000,000
Callaway refueling and maintenance outage costs
Regulatory assets:
Total regulatory assets	32,000,000	13,000,000
Callaway refueling and maintenance outage costs \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 32,000,000	13,000,000
Regulatory liabilities:
Regulatory asset, amortization period	18 months
Callaway refueling and maintenance outage costs \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 0	0
Unamortized loss on reacquired debt
Regulatory assets:
Total regulatory assets	44,000,000	47,000,000
Unamortized loss on reacquired debt \| Ameren Missouri
Regulatory assets:
Total regulatory assets	40,000,000	42,000,000
Unamortized loss on reacquired debt \| Ameren Illinois
Regulatory assets:
Total regulatory assets	4,000,000	5,000,000
Environmental cost riders
Regulatory assets:
Total regulatory assets	46,000,000	43,000,000
Environmental cost riders \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Environmental cost riders \| Ameren Illinois
Regulatory assets:
Total regulatory assets	46,000,000	43,000,000
Storm costs
Regulatory assets:
Total regulatory assets	15,000,000	18,000,000
Storm costs \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Storm costs \| Ameren Illinois
Regulatory assets:
Total regulatory assets	15,000,000	18,000,000
Customer generation rebate program
Regulatory assets:
Total regulatory assets	141,000,000	89,000,000
Customer generation rebate program \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
Customer generation rebate program \| Ameren Illinois
Regulatory assets:
Total regulatory assets	141,000,000	89,000,000
PISA
Regulatory assets:
Total regulatory assets	558,000,000	464,000,000
PISA \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 558,000,000	464,000,000
Regulatory liabilities:
Regulatory asset, amortization period	20 years
PISA \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 0	0
Rush Island Energy Center securitization
Regulatory assets:
Total regulatory assets	443,000,000	465,000,000
Rush Island Energy Center securitization \| Ameren Missouri
Regulatory assets:
Total regulatory assets	443,000,000	465,000,000
Rush Island Energy Center securitization \| Ameren Illinois
Regulatory assets:
Total regulatory assets	0	0
RESRAM
Regulatory assets:
Total regulatory assets	44,000,000	51,000,000
RESRAM \| Ameren Missouri
Regulatory assets:
Total regulatory assets	44,000,000	51,000,000
RESRAM \| Ameren Illinois
Regulatory assets:
Total regulatory assets	0	0
Certain Meramec Energy Center costs
Regulatory assets:
Total regulatory assets	14,000,000	26,000,000
Certain Meramec Energy Center costs \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 14,000,000	26,000,000
Regulatory liabilities:
Regulatory asset, amortization period	5 years
Certain Meramec Energy Center costs \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 0	0
FEJA energy-efficiency rider
Regulatory assets:
Total regulatory assets	624,000,000	576,000,000
FEJA energy-efficiency rider \| Ameren Missouri
Regulatory assets:
Total regulatory assets	0	0
FEJA energy-efficiency rider \| Ameren Illinois
Regulatory assets:
Total regulatory assets	624,000,000	576,000,000
Property Tax Tracker
Regulatory assets:
Total regulatory assets	18,000,000	22,000,000
Property Tax Tracker \| Ameren Missouri
Regulatory assets:
Total regulatory assets	$ 18,000,000	22,000,000
Property Tax Tracker \| Ameren Missouri \| Electric
Regulatory liabilities:
Regulatory asset, amortization period	3 years
Property Tax Tracker \| Ameren Missouri \| Natural gas
Regulatory liabilities:
Regulatory asset, amortization period	5 years
Property Tax Tracker \| Ameren Illinois
Regulatory assets:
Total regulatory assets	$ 0	0
Other regulatory assets
Regulatory assets:
Total regulatory assets	83,000,000	134,000,000
Other regulatory assets \| Ameren Missouri
Regulatory assets:
Total regulatory assets	48,000,000	56,000,000
Other regulatory assets \| Ameren Illinois
Regulatory assets:
Total regulatory assets	34,000,000	78,000,000
Over-recovered Illinois electric power costs
Regulatory liabilities:
Total regulatory liabilities	85,000,000	34,000,000
Over-recovered Illinois electric power costs \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	0	0
Over-recovered Illinois electric power costs \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	$ 85,000,000	34,000,000
Amortization period	1 year
Over-recovered PGA
Regulatory liabilities:
Total regulatory liabilities	$ 42,000,000	35,000,000
Over-recovered PGA \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	3,000,000	2,000,000
Over-recovered PGA \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	39,000,000	33,000,000
MTM derivative gains
Regulatory liabilities:
Total regulatory liabilities	16,000,000	16,000,000
MTM derivative gains \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	12,000,000	10,000,000
MTM derivative gains \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	4,000,000	6,000,000
Cost of removal
Regulatory liabilities:
Total regulatory liabilities	2,511,000,000	2,294,000,000
Cost of removal \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	1,203,000,000	1,118,000,000
Cost of removal \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	1,230,000,000	1,115,000,000
AROs
Regulatory liabilities:
Total regulatory liabilities	841,000,000	691,000,000
AROs \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	841,000,000	691,000,000
AROs \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	0	0
Pension and postretirement benefit costs
Regulatory liabilities:
Total regulatory liabilities	467,000,000	358,000,000
Pension and postretirement benefit costs \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	230,000,000	202,000,000
Pension and postretirement benefit costs \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	237,000,000	156,000,000
Pension and postretirement benefit costs tracker
Regulatory liabilities:
Total regulatory liabilities	9,000,000	70,000,000
Pension and postretirement benefit costs tracker \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	$ 9,000,000	70,000,000
Regulatory liability, amortization period	4 years
Pension and postretirement benefit costs tracker \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	$ 0	0
Renewable energy credits and zero emission credits
Regulatory liabilities:
Total regulatory liabilities	699,000,000	586,000,000
Renewable energy credits and zero emission credits \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	0	0
Renewable energy credits and zero emission credits \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	699,000,000	586,000,000
Certain Rush Island Energy Center Costs
Regulatory liabilities:
Total regulatory liabilities	31,000,000	66,000,000
Certain Rush Island Energy Center Costs \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	31,000,000	66,000,000
Certain Rush Island Energy Center Costs \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	0	0
Rush Island Energy Center base rate revenue deferral
Regulatory liabilities:
Total regulatory liabilities	31,000,000	13,000,000
Rush Island Energy Center base rate revenue deferral \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	$ 31,000,000	13,000,000
Regulatory liability, amortization period	3 years
Rush Island Energy Center base rate revenue deferral \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	$ 0	0
Other regulatory liabilities
Regulatory liabilities:
Total regulatory liabilities	94,000,000	50,000,000
Other regulatory liabilities \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	24,000,000	1,000,000
Other regulatory liabilities \| Ameren Illinois
Regulatory liabilities:
Total regulatory liabilities	$ 67,000,000	43,000,000
FAC adjustments \| Ameren Missouri
Regulatory liabilities:
Accumulation period	4 months
Regulatory asset, amortization period	8 months
Asset Retirement Obligation - Nuclear decommissioning trust fund balance \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	$ 1,526,000,000	1,342,000,000
Asset Retirement Obligation - removal costs \| Ameren Missouri
Regulatory liabilities:
Total regulatory liabilities	$ 685,000,000	$ 651,000,000
Minimum \| FEJA energy-efficiency rider \| Ameren Illinois
Regulatory liabilities:
Regulatory asset, amortization period	1 year
Maximum \| FEJA energy-efficiency rider \| Ameren Illinois
Regulatory liabilities:
Regulatory asset, amortization period	13 years

Accumulation period for regulatory assets and liabilities.

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Amortization period of a regulatory asset or liability

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No definition available.

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- Definition

Deferral percentage of the depreciation expense on certain property, plant, and equipment placed in-service and not included in base rates.

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No definition available.

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Weighted-Average Amortization Period of regulatory assets and liabilities.

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No definition available.

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- Definition

The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
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-Topic 230
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-Paragraph 2
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-Publisher FASB
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- Definition

Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
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-Name Accounting Standards Codification
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- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

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- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

+ Details

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
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-Paragraph 1
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- References

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Amortization period for the recovery of regulatory liability, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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