Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets:
Cash and cash equivalents	$ 7	$ 25
Advances to money pool	96	106
Accounts receivable - affiliates	525	494
Miscellaneous accounts and notes receivable	96	106
Total current assets	2,264	2,181
Other assets	1,123	921
Total assets	44,598	40,830
Liabilities and Shareholders' Equity:
Long-Term Debt, Current Maturities	317	849
Short-term debt	1,143	536
Accounts and wages payable	1,059	1,136
Other current liabilities	475	501
Total current liabilities	3,413	3,345
Long-term debt, net	17,262	15,121
Other deferred credits and liabilities	487	426
Commitments and Contingencies (Note 4)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 269.9 and 266.3, respectively	3	3
Other paid-in capital, principally premium on common stock	7,513	7,216
Retained earnings	4,604	4,136
Accumulated other comprehensive loss	(6)	(6)
Total shareholders’ equity	12,243	11,478	$ 10,637
TOTAL LIABILITIES AND EQUITY	$ 44,598	$ 40,830
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	269,900,000	266,300,000	262,000,000.0	257,700,000
Ameren (parent)
Assets:
Cash and cash equivalents	$ 0	$ 16
Derivative Asset, Current	3	0
Total current assets	182	665
Investments in subsidiaries	16,262	14,573
Debt Securities, Noncurrent	44	0
Accumulated deferred income taxes, net	98	44
Other assets	155	149
Total assets	16,741	15,431
Liabilities and Shareholders' Equity:
Long-Term Debt, Current Maturities	0	450
Short-term debt	1,055	0
Taxes accrued	7	10
Other current liabilities	54	45
Total current liabilities	1,165	607
Long-term debt, net	3,383	3,379
Pension and other postretirement benefits	18	19
Other deferred credits and liabilities	73	77
Total liabilities	4,639	4,082
Commitments and Contingencies (Note 4)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 269.9 and 266.3, respectively	3	3
Other paid-in capital, principally premium on common stock	7,513	7,216
Retained earnings	4,592	4,136
Accumulated other comprehensive loss	(6)	(6)
Total shareholders’ equity	12,102	11,349
TOTAL LIABILITIES AND EQUITY	$ 16,741	$ 15,431
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	269,900,000	266,300,000
Ameren (parent) | Related Party
Assets:
Advances to money pool	$ 103	$ 598
Accounts receivable - affiliates	41	20
Miscellaneous accounts and notes receivable	103	598
Liabilities and Shareholders' Equity:
Accounts and wages payable	49	100
Ameren (parent) | Nonrelated Party
Assets:
Advances to money pool	35	31
Miscellaneous accounts and notes receivable	35	31
Liabilities and Shareholders' Equity:
Accounts and wages payable	$ 0	$ 2