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Fair Value Measurements (Tables) | 12 Months Ended
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Dec. 31, 2023
Fair Value Disclosures [Abstract] |
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis | The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022:
|  | December 31, 2023 |  |  | December 31, 2022 |
|  | Level 1 | Level 2 | Level 3 | Total |  |  | Level 1 | Level 2 | Level 3 | Total |
Assets: |  |  |  |  |  |  |  |  |  |  |
Ameren Missouri |  |  |  |  |  |  |  |  |  |  |
| Derivative assets – commodity contracts: |  |  |  |  |  |  |  |  |  |  |
| Fuel oils | $ | 2 |  | $ | — |  | $ | — |  | $ | 2 |  |  |  | $ | 16 |  | $ | — |  | $ | — |  | $ | 16 |  |
| Natural gas | — |  | 3 |  | — |  | 3 |  |  |  | 1 |  | 15 |  | — |  | 16 |  |
| Power | — |  | — |  | 5 |  | 5 |  |  |  | — |  | — |  | 14 |  | 14 |  |
| Uranium | — |  | — |  | 9 |  | 9 |  |  |  | — |  | — |  | 3 |  | 3 |  |
| Total derivative assets – commodity contracts | $ | 2 |  | $ | 3 |  | $ | 14 |  | $ | 19 |  |  |  | $ | 17 |  | $ | 15 |  | $ | 17 |  | $ | 49 |  |
| Nuclear decommissioning trust fund: |  |  |  |  |  |  |  |  |  |  |
| Equity securities: |  |  |  |  |  |  |  |  |  |  |
| U.S. large capitalization | $ | 787 |  | $ | — |  | $ | — |  | $ | 787 |  |  |  | $ | 618 |  | $ | — |  | $ | — |  | $ | 618 |  |
| Debt securities: |  |  |  |  |  |  |  |  |  |  |
| U.S. Treasury and agency securities | — |  | 150 |  | — |  | 150 |  |  |  | — |  | 137 |  | — |  | 137 |  |
| Corporate bonds | — |  | 136 |  | — |  | 136 |  |  |  | — |  | 122 |  | — |  | 122 |  |
| Other | — |  | 68 |  | — |  | 68 |  |  |  | — |  | 70 |  | — |  | 70 |  |
| Total nuclear decommissioning trust fund | $ | 787 |  | $ | 354 |  | $ | — |  | $ | 1,141 |  | (a) |  | $ | 618 |  | $ | 329 |  | $ | — |  | $ | 947 |  | (a)
| Total Ameren Missouri | $ | 789 |  | $ | 357 |  | $ | 14 |  | $ | 1,160 |  |  |  | $ | 635 |  | $ | 344 |  | $ | 17 |  | $ | 996 |  |
Ameren Illinois |  |  |  |  |  |  |  |  |  |  |
| Derivative assets – commodity contracts: |  |  |  |  |  |  |  |  |  |  |
| Natural gas | $ | — |  | $ | 1 |  | $ | 2 |  | $ | 3 |  |  |  | $ | 1 |  | $ | 28 |  | $ | 5 |  | $ | 34 |  |
| Power | — |  | — |  | — |  | — |  |  |  | — |  | — |  | 6 |  | 6 |  |
| Total Ameren Illinois | $ | — |  | $ | 1 |  | $ | 2 |  | $ | 3 |  |  |  | $ | 1 |  | $ | 28 |  | $ | 11 |  | $ | 40 |  |
Ameren |  |  |  |  |  |  |  |  |  |  |
| Derivative assets – commodity contracts(b) | $ | 2 |  | $ | 4 |  | $ | 16 |  | $ | 22 |  |  |  | $ | 18 |  | $ | 43 |  | $ | 28 |  | $ | 89 |  |
| Nuclear decommissioning trust fund(c) | 787 |  | 354 |  | — |  | 1,141 |  | (a) |  | 618 |  | 329 |  | — |  | 947 |  | (a)
| Total Ameren | $ | 789 |  | $ | 358 |  | $ | 16 |  | $ | 1,163 |  |  |  | $ | 636 |  | $ | 372 |  | $ | 28 |  | $ | 1,036 |  |
Liabilities: |  |  |  |  |  |  |  |  |  |  |
Ameren Missouri |  |  |  |  |  |  |  |  |  |  |
| Derivative liabilities – commodity contracts: |  |  |  |  |  |  |  |  |  |  |
| Fuel oils | $ | 2 |  | $ | — |  | $ | — |  | $ | 2 |  |  |  | $ | — |  | $ | — |  | $ | — |  | $ | — |  |
| Natural gas | $ | — |  | $ | 19 |  | $ | 3 |  | $ | 22 |  |  |  | $ | — |  | $ | 6 |  | $ | 3 |  | $ | 9 |  |
| Power | — |  | — |  | 1 |  | 1 |  |  |  | 57 |  | — |  | 2 |  | 59 |  |
| Total Ameren Missouri | $ | 2 |  | $ | 19 |  | $ | 4 |  | $ | 25 |  |  |  | $ | 57 |  | $ | 6 |  | $ | 5 |  | $ | 68 |  |
Ameren Illinois |  |  |  |  |  |  |  |  |  |  |
| Derivative liabilities – commodity contracts: |  |  |  |  |  |  |  |  |  |  |
| Natural gas | $ | 4 |  | $ | 60 |  | $ | 11 |  | $ | 75 |  |  |  | $ | — |  | $ | 19 |  | $ | 10 |  | $ | 29 |  |
| Power | — |  | — |  | 68 |  | 68 |  |  |  | — |  | — |  | 39 |  | 39 |  |
| Total Ameren Illinois | $ | 4 |  | $ | 60 |  | $ | 79 |  | $ | 143 |  |  |  | $ | — |  | $ | 19 |  | $ | 49 |  | $ | 68 |  |
Ameren |  |  |  |  |  |  |  |  |  |  |
| Derivative liabilities – commodity contracts(b) | $ | 6 |  | $ | 79 |  | $ | 83 |  | $ | 168 |  |  |  | $ | 57 |  | $ | 25 |  | $ | 54 |  | $ | 136 |  |
(a)Balance excludes $9 million and $11 million of cash and cash equivalents, receivables, payables, and accrued income, net for December 31, 2023 and 2022, respectively. (b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity. (c)See the Ameren Missouri section of the table for a breakout of Ameren’s nuclear decommissioning trust fund by investment type.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy | The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the years ended December 31, 2023 and 2022:
| 2023 |  |  | 2022
| Ameren Missouri | Ameren Illinois | Ameren |  |  | Ameren Missouri | Ameren Illinois | Ameren
Beginning balance at January 1 | $ | 12 |  | $ | (33) |  | $ | (21) |  |  |  | $ | (15) |  | $ | (117) |  | $ | (132) |
Realized and unrealized gains (losses) included in regulatory assets/liabilities | 1 |  | (48) |  | (47) |  |  |  | (45) |  | 92 |  | 47 |
Settlements | (9) |  | 13 |  | 4 |  |  |  | 72 |  | (8) |  | 64 |
Ending balance at December 31 | $ | 4 |  | $ | (68) |  | $ | (64) |  |  |  | $ | 12 |  | $ | (33) |  | $ | (21) |
Change in unrealized gains (losses) related to assets/liabilities held at December 31 | $ | 4 |  | $ | (36) |  | $ | (32) |  |  |  | $ | 12 |  | $ | 75 |  | $ | 87 |
Fair Value Inputs, Assets and Liabilities, Quantitative Information | The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of December 31, 2023 and 2022:
|  | Fair Value |  |  |  |  | Weighted Average(b)
| Commodity | Assets | Liabilities |  | Valuation Technique(s) | Unobservable Input(a) | Range
2023 | Power(c) | $ | 5 |  | $ | (69) |  |  | Discounted cash flow | Average forward peak and off-peak pricing – forwards/swaps ($/MWh) | 31 – 65 | 43
|  |  |  |  |  | Nodal basis ($/MWh) | (8) – (1) | (5)
2022 | Power(d) | $ | 20 |  | $ | (41) |  |  | Discounted cash flow | Average forward peak and off-peak pricing – forwards/swaps ($/MWh) | 38 – 89 | 51
|  |  |  |  |  | Nodal basis ($/MWh) | (10) – (1) | (4)
|  |  |  |  |  | Trend rate (%) | 0– 1 | 0
(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement. (b)Unobservable inputs were weighted by relative fair value. (c)Valuations use visible forward prices adjusted for nodal-to-hub basis differentials. (d)Valuations through 2031 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2031 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] | The following table sets forth, by level within the fair value hierarchy, the carrying amount and fair value of financial assets and liabilities disclosed, but not carried, at fair value as of December 31, 2023 and 2022:
| Carrying Amount |  | Fair Value |  |
|  | Level 1 |  | Level 2 |  | Level 3 |  | Total
| December 31, 2023
Ameren: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 272 |  |  | $ | 272 |  |  | $ | — |  |  | $ | — |  |  | $ | 272 |
Short-term debt | 536 |  |  | — |  |  | 536 |  |  | — |  |  | 536 |
Long-term debt (including current portion) | 15,970 |  | (a) | — |  |  | 14,366 |  |  | 467 |  | (b) | 14,833 |
Ameren Missouri: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 10 |  |  | $ | 10 |  |  | $ | — |  |  | $ | — |  |  | $ | 10 |
Short-term debt | 170 |  |  | — |  |  | 170 |  |  | — |  |  | 170 |
Borrowings from money pool | 306 |  |  | — |  |  | 306 |  |  | — |  |  | 306 |
Long-term debt (including current portion) | 6,341 |  | (a) | — |  |  | 5,800 |  |  | — |  |  | 5,800 |
Ameren Illinois: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 234 |  |  | $ | 234 |  |  | $ | — |  |  | $ | — |  |  | $ | 234 |
Short-term debt | 366 |  |  | — |  |  | 366 |  |  | — |  |  | 366 |
Borrowings from money pool | 135 |  |  | — |  |  | 135 |  |  | — |  |  | 135 |
Long-term debt (including current portion) | 5,232 |  | (a) | — |  |  | 4,867 |  |  | — |  |  | 4,867 |
| December 31, 2022
Ameren: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 216 |  |  | $ | 216 |  |  | $ | — |  |  | $ | — |  |  | $ | 216 |
Investments in industrial development revenue bonds(c) | 240 |  |  | — |  |  | 240 |  |  | — |  |  | 240 |
Short-term debt | 1,070 |  |  | — |  |  | 1,070 |  |  | — |  |  | 1,070 |
Long-term debt (including current portion)(c) | 14,025 |  | (a) | — |  |  | 11,989 |  |  | 464 |  | (b) | 12,453 |
Ameren Missouri: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 13 |  |  | $ | 13 |  |  | $ | — |  |  | $ | — |  |  | $ | 13 |
Investments in industrial development revenue bonds(c) | 240 |  |  | — |  |  | 240 |  |  | — |  |  | 240 |
Short-term debt | 329 |  |  | — |  |  | 329 |  |  | — |  |  | 329 |
Long-term debt (including current portion)(c) | 6,086 |  | (a) | — |  |  | 5,365 |  |  | — |  |  | 5,365 |
Ameren Illinois: |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and restricted cash | $ | 191 |  |  | $ | 191 |  |  | $ | — |  |  | $ | — |  |  | $ | 191 |
Short-term debt | 264 |  |  | — |  |  | 264 |  |  | — |  |  | 264 |
Long-term debt (including current portion) | 4,835 |  | (a) | — |  |  | 4,320 |  |  | — |  |  | 4,320 |
(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $111 million, $45 million, and $47 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2023. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $99 million, $41 million, and $44 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2022. (b)The Level 3 fair value amount consists of ATXI’s senior unsecured notes. (c)Ameren and Ameren Missouri had investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Investments in industrial development revenue bonds,” as of December 31, 2022, respectively, that were equal to the finance obligation for the Audrain CT energy center. As of December 31, 2022, the carrying amount of the investments in industrial development revenue bonds and the finance obligations approximated fair value. The financing obligation for the Audrain CT Energy Center was settled in January 2023. See Note 5 – Long-term Debt and Equity Financings for additional information on these agreements.

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