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Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2023 | Mar. 31, 2022
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 1,175 | $ 789
Weighted-average interest rate | 4.88% | 0.41%
Short-term Debt, Maximum Amount Outstanding During Period | $ 1,381 | $ 1,101
Peak interest rate | 5.60% | 1.15%
Parent Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 506 | $ 282
Weighted-average interest rate | 4.89% | 0.41%
Short-term Debt, Maximum Amount Outstanding During Period | $ 728 | $ 466
Peak interest rate | 5.55% | 1.05%
Union Electric Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 436 | $ 408
Weighted-average interest rate | 4.86% | 0.44%
Short-term Debt, Maximum Amount Outstanding During Period | $ 592 | $ 539
Peak interest rate | 5.55% | 1.06%
Ameren Illinois Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 233 | $ 99
Weighted-average interest rate | 4.89% | 0.33%
Short-term Debt, Maximum Amount Outstanding During Period | $ 325 | $ 142
Peak interest rate | 5.60% | 1.15%

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