Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
2025	$ 317
2026	974
2027	974
2028	966
2029	1,207
Thereafter	13,361
Total	17,799
Ameren (parent)
Debt Instrument [Line Items]
2025	0
2026	950
2027	500
2028	450
2029	700
Thereafter	800
Total	3,400
Unamortized discount, premium, and debt issuance costs	17
Ameren Missouri
Debt Instrument [Line Items]
2025	17
2026	24
2027	424
2028	26
2029	477
Thereafter	6,857
Total	7,825
Unamortized discount, premium, and debt issuance costs	79
Ameren Illinois
Debt Instrument [Line Items]
2025	300
2026	0
2027	0
2028	490
2029	0
Thereafter	5,123
Total	5,913
Unamortized discount, premium, and debt issuance costs	61
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
2025	0
2026	0
2027	50
2028	0
2029	30
Thereafter	581
Total	661
Unamortized discount, premium, and debt issuance costs	2
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036
Debt Instrument [Line Items]
Debt instrument face amount	75	$ 75
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036 \| Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Thereafter	30
Unsecured Debt \| Ameren Transmission Company of Illinois \| 2.45% Senior unsecured notes due 2036 \| Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Thereafter	45
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050
Debt Instrument [Line Items]
Debt instrument face amount	351	$ 400
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Thereafter	50
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Four
Debt Instrument [Line Items]
Thereafter	49
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Five
Debt Instrument [Line Items]
Thereafter	50
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Six
Debt Instrument [Line Items]
Thereafter	49
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Seven
Debt Instrument [Line Items]
Thereafter	77
Unsecured Debt \| Ameren Transmission Company of Illinois \| 3.43% Senior unsecured notes due 2050 \| Debt Instrument, Redemption, Period Eight
Debt Instrument [Line Items]
Thereafter	$ 76

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