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Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Supplemental Cash Flow Information [Line Items] |  |  |
Accrued capital expenditures | $ 622 | $ 480 | $ 518
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 160 | 165 | 167
Return on investment in industrial development revenue bonds | 0 | 0 | 240
Stock Issued |  | 16 |
Termination of a financing obligation | 0 | 0 | 240
Ameren (parent) |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 25 | 16 | 40
Issuance of common stock for stock-based compensation |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 25 | 16 | 40
Issuance of common stock under the DRPlus | Ameren (parent) |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 7 | 7 | 7
Ameren Missouri |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Accrued capital expenditures | 355 | 303 | 270
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 160 | 165 | 167
Return on investment in industrial development revenue bonds | 0 | 0 | 240
Termination of a financing obligation | 0 | 0 | 240
Ameren Missouri | Issuance of common stock for stock-based compensation |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 0 | 0 | 0
Ameren Missouri | Issuance of common stock under the DRPlus |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 0 | 0 | 0
Ameren Illinois |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Accrued capital expenditures | 210 | 157 | 212
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 0 | 0 | 0
Return on investment in industrial development revenue bonds | 0 | 0 | 0
Termination of a financing obligation | 0 | 0 | 0
Ameren Illinois | Issuance of common stock for stock-based compensation |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | 0 | 0 | 0
Ameren Illinois | Issuance of common stock under the DRPlus |  |  |
Supplemental Cash Flow Information [Line Items] |  |  |
Stock Issued | $ 0 | $ 0 | $ 0

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- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-4 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-3 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-5 + Details
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