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Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2022 | Jun. 30, 2021
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 702 | $ 782
Weighted-average interest rate | 0.75% | 0.23%
Short-term Debt, Maximum Amount Outstanding During Period | $ 1,101 | $ 1,134
Peak interest rate | 2.05% | 0.33%
Parent Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 374 | $ 388
Weighted-average interest rate | 0.87% | 0.24%
Short-term Debt, Maximum Amount Outstanding During Period | $ 595 | $ 650
Peak interest rate | 2.05% | 0.33%
Union Electric Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 271 | $ 183
Weighted-average interest rate | 0.65% | 0.22%
Short-term Debt, Maximum Amount Outstanding During Period | $ 539 | $ 546
Peak interest rate | 2.05% | 0.25%
Ameren Illinois Company |  |
Short-term Debt [Line Items] |  |
Average daily amount outstanding | $ 57 | $ 211
Weighted-average interest rate | 0.47% | 0.22%
Short-term Debt, Maximum Amount Outstanding During Period | $ 142 | $ 485
Peak interest rate | 2.05% | 0.25%

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