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Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Dec. 31, 2022
Allowance for Doubtful Accounts Receivable [Roll Forward] |  |  |  |  |
Beginning of period | $ 39 | $ 30 | $ 31 | $ 29 |
Bad debt expense | 18 | 14 | 41 | 23 |
Charged to other accounts | 2 | 1 | 3 | 3 |
Net write-offs | (26) | (14) | (42) | (24) |
End of period | 33 | $ 31 | 33 | $ 31 |
Payables for purchased receivables | $ 50 |  | $ 50 |  | $ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement | 17.00% | 17.00% | 17.00% | 17.00% |
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement | $ 106 | $ 117 | $ 106 | $ 117 |
Union Electric Company |  |  |  |  |
Allowance for Doubtful Accounts Receivable [Roll Forward] |  |  |  |  |
Beginning of period | 12 | 12 | 13 | 13 |
Bad debt expense | 5 | 3 | 9 | 6 |
Net write-offs | (5) | (3) | (10) | (7) |
End of period | $ 12 | $ 12 | $ 12 | $ 12 |
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement | 8.00% | 12.00% | 8.00% | 12.00% |
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement | $ 25 | $ 39 | $ 25 | $ 39 |
Ameren Illinois Company |  |  |  |  |
Allowance for Doubtful Accounts Receivable [Roll Forward] |  |  |  |  |
Beginning of period | 27 | 18 | 18 | 16 |
Bad debt expense | 13 | 11 | 32 | 17 |
Charged to other accounts | 2 | 1 | 3 | 3 |
Net write-offs | (21) | (11) | (32) | (17) |
End of period | 21 | $ 19 | 21 | $ 19 |
Payables for purchased receivables | $ 50 |  | $ 50 |  | $ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement | 26.00% | 21.00% | 26.00% | 21.00% |
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement | $ 81 | $ 78 | $ 81 | $ 78 |

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