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, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 437
Cash and cash equivalents	328	$ 272	$ 216	$ 155
Fair Value	1,342	1,150
Cash and cash equivalents	7	25
Ameren Missouri
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	625	582
Cash and cash equivalents	17	10	$ 13	$ 8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	742	606
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	25	38
Fair Value	1,342	1,150
Cash and cash equivalents	0	0
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	1,342	1,150
Ameren Missouri | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	437	382
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2	3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	17	31
Fair Value	422	354
Ameren Missouri | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	179	191
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	740	603
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	8	7
Equity Securities, FV-NI	911	787
Ameren Missouri | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	10	5
Cash and cash equivalents	0	0
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents	0	0
Cash and cash equivalents	10	5
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	(1)	4
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	$ (1)	$ 4