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Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 488
Cash and cash equivalents	420	$ 328	$ 272	$ 216
Fair Value	1,526	1,342
Cash and cash equivalents	13	7
Ameren Missouri
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	679	625
Cash and cash equivalents	68	17	$ 10	$ 13
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	865	742
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	18	25
Fair Value	1,526	1,342
Cash and cash equivalents	6	0
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	1,526	1,342
Ameren Missouri | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	488	437
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	7	2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	9	17
Fair Value	486	422
Ameren Missouri | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	179	179
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	858	740
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	9	8
Equity Securities, FV-NI	1,028	911
Ameren Missouri | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	8	10
Cash and cash equivalents	0	0
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents	0	0
Cash and cash equivalents	8	10
Ameren Missouri | Other Debt And Equity Securities
Nuclear Waste Matters [Line Items]
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Cost Basis	4	(1)
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Gain, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Loss, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Fair Value	$ 4	$ (1)

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