Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets:
Cash and cash equivalents	$ 25	$ 10
Advances to money pool	106	54
Accounts receivable - affiliates	494	600
Miscellaneous accounts and notes receivable	106	54
Other current assets	125	155
Total current assets	2,181	2,668
Other assets	921	768
Total assets	40,830	37,904
Liabilities and Shareholders' Equity:
Current maturities of long-term debt	849	340
Short-term debt	536	1,070
Accounts and wages payable	1,136	1,159
Other current liabilities	648	682
Total current liabilities	3,345	3,366
Long-term debt, net	15,121	13,685
Other deferred credits and liabilities	426	340
Commitments and Contingencies (Note 4)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 266.3 and 262.0, respectively	3	3
Other paid-in capital, principally premium on common stock	7,216	6,860
Retained earnings	4,136	3,646
Accumulated other comprehensive income (loss)	(6)	(1)
Total shareholders’ equity	11,478	10,637	$ 9,829
TOTAL LIABILITIES AND EQUITY	$ 40,830	$ 37,904
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	266,300,000	262,000,000.0	257,700,000	253,300,000
Ameren (parent)
Assets:
Cash and cash equivalents	$ 16	$ 0
Total current assets	665	138
Investments in subsidiaries	14,573	13,394
Accumulated deferred income taxes, net	44	46
Other assets	149	137
Total assets	15,431	13,715
Liabilities and Shareholders' Equity:
Current maturities of long-term debt	450	0
Short-term debt	0	477
Accounts and wages payable	2
Taxes accrued	10	5
Other current liabilities	45	41
Total current liabilities	607	575
Long-term debt, net	3,379	2,536
Pension and other postretirement benefits	19	19
Other deferred credits and liabilities	77	77
Total liabilities	4,082	3,207
Commitments and Contingencies (Note 4)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 266.3 and 262.0, respectively	3	3
Other paid-in capital, principally premium on common stock	7,216	6,860
Retained earnings	4,136	3,646
Accumulated other comprehensive income (loss)	(6)	(1)
Total shareholders’ equity	11,349	10,508
TOTAL LIABILITIES AND EQUITY	$ 15,431	$ 13,715
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	266,300,000	262,000,000.0
Ameren (parent) | Related Party
Assets:
Advances to money pool	$ 598	$ 68
Accounts receivable - affiliates	20	59
Miscellaneous accounts and notes receivable	598	68
Liabilities and Shareholders' Equity:
Accounts and wages payable	100	52
Ameren (parent) | Nonrelated Party
Assets:
Advances to money pool	31	11
Miscellaneous accounts and notes receivable	$ 31	$ 11