Supplemental Information (Schedule of Excise Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Line Items]
Excise Tax Expense	$ 329	$ 299	$ 287
Ameren Missouri
Accounting Policies [Line Items]
Excise Tax Expense	189	169	166
Ameren Illinois
Accounting Policies [Line Items]
Excise Tax Expense	$ 140	$ 130	$ 121

The amount of excise and sales taxes included in sales and revenues, which are then deducted as a cost of sales. Includes excise taxes, which are applied to specific types of transactions or items (such as gasoline or alcohol); and sales, use and value added taxes, which are applied to a broad class of revenue-producing transactions involving a wide range of goods and services.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Name:	us-gaap_ExciseAndSalesTaxes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration