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Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Oct. 31, 2024 | Sep. 30, 2024 | Aug. 31, 2024 | Jun. 30, 2024 | Apr. 30, 2024 | Jan. 31, 2024 | Dec. 31, 2023 | Nov. 30, 2023 | May 31, 2023 | Mar. 31, 2023
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Less: Maturities due within one year | $ (317) |  |  |  |  |  |  | $ (849) |  |  |
Long-Term Debt, Excluding Current Maturities | 17,262 |  |  |  |  |  |  | 15,121 |  |  |
Thereafter | 13,361 |  |  |  |  |  |  |  |  |  |
Ameren (parent) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total long-term debt, gross | 3,400 |  |  |  |  |  |  | 3,850 |  |  |
Less: Unamortized discount and premium | (3) |  |  |  |  |  |  | (4) |  |  |
Less: Unamortized debt issuance costs | (14) |  |  |  |  |  |  | (17) |  |  |
Long-Term Debt, Excluding Current Maturities | 3,383 |  |  |  |  |  |  | 3,379 |  |  |
Thereafter | 800 |  |  |  |  |  |  |  |  |  |
Ameren Missouri |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total long-term debt, gross | 7,825 |  |  |  |  |  |  | 6,399 |  |  |
Less: Unamortized discount and premium | (17) |  |  |  |  |  |  | (13) |  |  |
Less: Unamortized debt issuance costs | (62) |  |  |  |  |  |  | (45) |  |  |
Less: Maturities due within one year | (17) |  |  |  |  |  |  | (350) |  |  |
Long-Term Debt, Excluding Current Maturities | 7,671 |  |  |  |  |  |  | 5,991 |  |  |
Thereafter | 6,857 |  |  |  |  |  |  |  |  |  |
Ameren Missouri | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Less: Unamortized debt issuance costs | (1) |  |  |  |  |  |  | 0 |  |  |
Long-Term Debt, Excluding Current Maturities | 57 |  |  |  |  |  |  | 0 |  |  |
Ameren Illinois |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total long-term debt, gross | 5,913 |  |  |  |  |  |  | 5,288 |  |  |
Less: Unamortized discount and premium | (10) |  |  |  |  |  |  | (9) |  |  |
Less: Unamortized debt issuance costs | (51) |  |  |  |  |  |  | (47) |  |  |
Less: Maturities due within one year | (300) |  |  |  |  |  |  | 0 |  |  |
Long-Term Debt, Excluding Current Maturities | 5,549 |  |  |  |  |  |  | 5,232 |  |  |
Thereafter | 5,123 |  |  |  |  |  |  |  |  |  |
Ameren Illinois | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt, Excluding Current Maturities | 3 |  |  |  |  |  |  | 0 |  |  |
Ameren Transmission Company of Illinois |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total long-term debt, gross | 661 |  |  |  |  |  |  | 570 |  |  |
Less: Unamortized debt issuance costs | (2) |  |  |  |  |  |  | (2) |  |  |
Less: Maturities due within one year | 0 |  |  |  |  |  |  | (49) |  |  |
Long-Term Debt, Excluding Current Maturities | 659 |  |  |  |  |  |  | 519 |  |  |
Thereafter | $ 581 |  |  |  |  |  |  |  |  |  |
Unsecured Debt | Ameren (parent) | 2.50% Senior unsecured notes due 2024 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.50% |  | 2.50% |  |  |  |  |  |  |  |
Debt instrument face amount | $ 0 |  | $ (450) |  |  |  |  | (450) |  |  |
Unsecured Debt | Ameren (parent) | 3.65% Senior unsecured notes due 2026 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.65% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (350) |  |  |  |  |  |  | (350) |  |  |
Unsecured Debt | Ameren (parent) | 5.70% Senior unsecured notes due 2026 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.70% |  |  |  |  |  |  |  | 5.70% |  |
Debt instrument face amount | $ (600) |  |  |  |  |  |  | (600) | $ (600) |  |
Unsecured Debt | Ameren (parent) | 1.95% Senior unsecured notes due 2027 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 1.95% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (500) |  |  |  |  |  |  | (500) |  |  |
Unsecured Debt | Ameren (parent) | 1.75% Senior unsecured notes due 2028 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 1.75% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (450) |  |  |  |  |  |  | (450) |  |  |
Unsecured Debt | Ameren (parent) | 5.00% Senior unsecured notes due 2029 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.00% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (700) |  |  |  |  |  |  | (700) |  |  |
Unsecured Debt | Ameren (parent) | 3.50% Senior unsecured notes due 2031 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.50% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (800) |  |  |  |  |  |  | (800) |  |  |
Unsecured Debt | Ameren Illinois | 4.95% First mortgage bonds due 2033 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  |  |  |  | 4.95% |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.45% Senior unsecured notes due 2036 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.45% |  |  |  |  |  |  |  |  |  |
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 | Senior Unsecured Notes, 5.17%, Due 2039 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.17% |  |  | 5.17% |  |  |  |  |  |  |
Debt instrument face amount | $ (70) |  |  | $ (70) |  |  |  | 0 |  |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.43% |  |  | 3.43% |  |  |  |  |  |  |
Debt instrument face amount | $ (351) |  |  |  |  |  |  | (400) |  |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.96% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (95) |  |  |  |  |  |  | (95) |  |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 | Debt Instrument, Redemption, Period One |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Thereafter | 45 |  |  |  |  |  |  |  |  |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 | Debt Instrument, Redemption, Period Two |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Thereafter | $ 50 |  |  |  |  |  |  |  |  |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 5.42%, Due 2053 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.42% |  |  | 5.42% |  |  |  |  |  |  |
Debt instrument face amount | $ (70) |  |  | $ (70) |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (58) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 3.50% senior secured notes due 2024 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.50% |  |  |  |  | 3.50% |  |  |  |  |
Debt instrument face amount | $ 0 |  |  |  |  | $ (350) |  | (350) |  |  |
Secured Debt | Ameren Missouri | 2.95% senior secured notes due 2027 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.95% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (400) |  |  |  |  |  |  | (400) |  |  |
Secured Debt | Ameren Missouri | 3.50% First mortgage bonds due 2029 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.50% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (450) |  |  |  |  |  |  | (450) |  |  |
Secured Debt | Ameren Missouri | 2.95% First mortgage bonds due 2030 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.95% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (465) |  |  |  |  |  |  | (465) |  |  |
Secured Debt | Ameren Missouri | 2.15% First mortgage bonds due 2032 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.15% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (525) |  |  |  |  |  |  | (525) |  |  |
Secured Debt | Ameren Missouri | First Mortgage Bonds 5.20% Due 2034 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.20% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (500) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 5.50% Senior secured notes due 2034 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.50% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (184) |  |  |  |  |  |  | (184) |  |  |
Secured Debt | Ameren Missouri | 5.30% Senior secured notes due 2037 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.30% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (300) |  |  |  |  |  |  | (300) |  |  |
Secured Debt | Ameren Missouri | 8.45% Senior secured notes due 2039 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 8.45% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (350) |  |  |  |  |  |  | (350) |  |  |
Secured Debt | Ameren Missouri | 4.85% Securitized Utility Tariff Bonds Due 2039 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.85% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (476) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 3.90% Senior secured notes due 2042 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.90% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (485) |  |  |  |  |  |  | (485) |  |  |
Secured Debt | Ameren Missouri | 3.65% Senior secured notes due 2045 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.65% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (400) |  |  |  |  |  |  | (400) |  |  |
Secured Debt | Ameren Missouri | 3.65% Senior secured notes due 2045 | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.65% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (7) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 4.00% First mortgage bonds due 2048 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.00% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (425) |  |  |  |  |  |  | (425) |  |  |
Secured Debt | Ameren Missouri | 3.25% First Mortgage bonds due 2049 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.25% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (330) |  |  |  |  |  |  | (330) |  |  |
Secured Debt | Ameren Missouri | 3.25% First Mortgage bonds due 2049 | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.25% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (33) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 2.625% First Mortgage bonds due 2051 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.625% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (550) |  |  |  |  |  |  | (550) |  |  |
Secured Debt | Ameren Missouri | 2.625% First Mortgage bonds due 2051 | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.625% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (4) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.90% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (525) |  |  |  |  |  |  | (525) |  |  |
Secured Debt | Ameren Missouri | First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.90% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (14) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Missouri | 5.45% First mortgage bonds due 2053 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.45% |  |  |  |  |  |  |  |  |  | 5.45%
Debt instrument face amount | $ (500) |  |  |  |  |  |  | (500) |  |  | $ (500)
Secured Debt | Ameren Missouri | First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.25% |  |  |  |  |  | 5.25% |  |  |  |
Debt instrument face amount | $ (350) |  |  |  |  |  | $ (350) | 0 |  |  |
Secured Debt | Ameren Missouri | First Mortgage Bonds, 5.125%, Due 2055 - $450 Issuance |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.125% | 5.125% |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (450) | $ (450) |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Illinois | Related Party |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (3) |  |  |  |  |  |  | 0 |  |  |
Secured Debt | Ameren Illinois | 3.25% First Mortgage bonds due 2025 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.25% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (300) |  |  |  |  |  |  | (300) |  |  |
Secured Debt | Ameren Illinois | 6.125% First Mortgage bonds due 2028 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 6.125% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (60) |  |  |  |  |  |  | (60) |  |  |
Secured Debt | Ameren Illinois | 3.80% First Mortgage bonds due 2028 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.80% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (430) |  |  |  |  |  |  | (430) |  |  |
Secured Debt | Ameren Illinois | 1.55% First Mortgage bonds due 2030 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 1.55% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (375) |  |  |  |  |  |  | (375) |  |  |
Secured Debt | Ameren Illinois | 3.85% First mortgage bonds due 2032 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.85% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (500) |  |  |  |  |  |  | (500) |  |  |
Secured Debt | Ameren Illinois | 4.95% First mortgage bonds due 2033 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.95% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (500) |  |  |  |  |  |  | (500) |  | $ (500) |
Secured Debt | Ameren Illinois | 6.70% First Mortgage bonds due 2036 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 6.70% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (61) |  |  |  |  |  |  | (61) |  |  |
Secured Debt | Ameren Illinois | 6.70% First Mortgage bonds due 2036 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Secured Debt | Ameren Illinois | 4.80% First Mortgage bonds due 2043 |  |  |  |  |  |  |  |  |  |  |
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.70% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (500) |  |  |  |  |  |  | (500) |  |  |
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Secured Debt | Ameren Illinois | 4.50% First Mortgage bonds due 2049 |  |  |  |  |  |  |  |  |  |  |
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Secured Debt | Ameren Illinois | 5.90% First mortgage bonds due 2052 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Secured Debt | Ameren Illinois | 5.55% First mortgage bonds due 2054 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.55% |  |  |  | 5.55% |  |  |  |  |  |
Debt instrument face amount | $ (625) |  |  |  | $ (625) |  |  | 0 |  |  |
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Missouri | 2.90% 1998 Series A due 2033 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
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Debt instrument face amount | $ (60) |  |  |  |  |  |  | (60) |  |  |
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Missouri | 2.90% 1998 Series B due 2033 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.90% |  |  |  |  |  |  |  |  |  |
Debt instrument face amount | $ (50) |  |  |  |  |  |  | (50) |  |  |
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Missouri | 2.75% 1998 Series C due 2033 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.75% |  |  |  |  |  |  |  |  |  |
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