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Retirement Benefits (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 USD ($) bond | Dec. 31, 2021 USD ($) | Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan |  | $ 377 | $ 717 |
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation, Change in Discount Rate |  | 2.55% |  |
Number of high-quality corporate bonds | bond |  | 850 |  |
Defined benefit plan estimated future employer contributions over next five years |  | $ 170 |  |
Collateralized loan percentage compared to asset's market value |  | 103.00% |  |
Securities Loaned |  | $ 239 | 374 |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan |  | $ (34) | $ 288 |
Expected return on plan assets |  | 6.50% | 6.50% | 7.00%
Pension Benefits | Forecast |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected return on plan assets | 6.75% |  |  |
Union Electric Company | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Future funding requirement, percentage |  | 40.00% |  |
Ameren Illinois Company | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Future funding requirement, percentage |  | 50.00% |  |

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- Definition The change in the interest rate used to adjust for the time value of money for the plan + References No definition available. + Details
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- Definition The employer's best estimate, as soon as it can be reasonably determined, of the contributions expected to be paid to the plan during the next five fiscal years beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions. + References No definition available. + Details
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- Definition Defined Benefit Plan Number of High Quality Bonds Used to Determine Yield Curve + References No definition available. + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920 + Details
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