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Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Nov. 30, 2023 | May 31, 2023 | Mar. 31, 2023 | Dec. 31, 2022 | Nov. 30, 2022 | Aug. 31, 2022 | Apr. 30, 2022
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Less: Maturities due within one year | $ (849) |  |  |  | $ (340) |  |  |
Long-term Debt, Net | 15,121 |  |  |  | 13,685 |  |  |
Thereafter | 12,118 |  |  |  |  |  |  |
Ameren (parent) |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Total long-term debt, gross | 3,850 |  |  |  | 2,550 |  |  |
Less: Unamortized discount and premium | (4) |  |  |  | (2) |  |  |
Less: Unamortized debt issuance costs | (17) |  |  |  | (12) |  |  |
Long-term Debt, Net | 3,379 |  |  |  | 2,536 |  |  |
Thereafter | 1,500 |  |  |  |  |  |  |
Ameren Missouri |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Total long-term debt, gross | 6,399 |  |  |  | 6,139 |  |  |
Less: Unamortized discount and premium | (13) |  |  |  | (12) |  |  |
Less: Unamortized debt issuance costs | (45) |  |  |  | (41) |  |  |
Less: Maturities due within one year | (350) |  |  |  | (240) |  |  |
Long-term Debt, Net | 5,991 |  |  |  | 5,846 |  |  |
Debt securities, held-to-maturity | 240 |  |  |  | 240 |  |  |
Thereafter | 5,649 |  |  |  |  |  |  |
Ameren Missouri | Audrain County Agreement - Audrain County Ct |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument face amount | 0 |  |  |  | 240 |  |  |
Ameren Illinois |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Total long-term debt, gross | 5,288 |  |  |  | 4,888 |  |  |
Less: Unamortized discount and premium | (9) |  |  |  | (9) |  |  |
Less: Unamortized debt issuance costs | (47) |  |  |  | (44) |  |  |
Less: Maturities due within one year | 0 |  |  |  | (100) |  |  |
Long-term Debt, Net | 5,232 |  |  |  | 4,735 |  |  |
Thereafter | 4,498 |  |  |  |  |  |  |
Ameren Transmission Company of Illinois |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Total long-term debt, gross | 570 |  |  |  | 570 |  |  |
Less: Unamortized debt issuance costs | (2) |  |  |  | (2) |  |  |
Less: Maturities due within one year | (49) |  |  |  | 0 |  |  |
Long-term Debt, Net | 519 |  |  |  | 568 |  |  |
Thereafter | $ 471 |  |  |  |  |  |  |
Unsecured Debt | Ameren (parent) | 2.50% Senior unsecured notes due 2024 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.50% |  |  |  |  |  |  |
Debt instrument face amount | $ 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 |  |  | 0 |  |  |
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 |  |  |  | 0 |  |  |
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 | 3.85% First mortgage bonds due 2032 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  | 3.85% |  |  |
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 | 3.43% Senior unsecured notes due 2050 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  | 3.43% |
Debt instrument face amount | $ 400 |  |  |  | 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% |  |  |  |  |  | 2.96% |
Debt instrument face amount | $ 95 |  |  |  | 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 |  |  |  |  |  |  |
Secured Debt | Ameren Missouri | 3.50% senior secured notes due 2024 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.50% |  |  |  |  |  |  |
Debt instrument face amount | $ 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 | 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 | 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 | 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 | 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 | First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.90% |  |  |  |  |  |  | 3.90%
Debt instrument face amount | $ 525 |  |  |  | 525 |  |  | $ 525
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 | 0 |  |  |
Secured Debt | Ameren Illinois | 0.375% First Mortgage bonds due 2023 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 0.375% |  |  |  |  |  |  |
Debt instrument face amount | $ 0 |  |  |  | 100 |  |  |
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 | 0.0385% |  |  |  |  |  |  |
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 | 0.0495% |  |  |  |  |  |  |
Debt instrument face amount | $ 500 |  | $ 500 |  | 0 |  |  |
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] |  |  |  |  |  |  |  |
Long-term debt interest rate | 6.70% |  |  |  |  |  |  |
Debt instrument face amount | $ 42 |  |  |  | 42 |  |  |
Secured Debt | Ameren Illinois | 4.80% First Mortgage bonds due 2043 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.80% |  |  |  |  |  |  |
Debt instrument face amount | $ 280 |  |  |  | 280 |  |  |
Secured Debt | Ameren Illinois | 4.30% First Mortgage bonds due 2044 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.30% |  |  |  |  |  |  |
Debt instrument face amount | $ 250 |  |  |  | 250 |  |  |
Secured Debt | Ameren Illinois | 4.15% First Mortgage bonds due 2046 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.15% |  |  |  |  |  |  |
Debt instrument face amount | $ 490 |  |  |  | 490 |  |  |
Secured Debt | Ameren Illinois | 3.70% First Mortgage bonds due 2047 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.70% |  |  |  |  |  |  |
Debt instrument face amount | $ 500 |  |  |  | 500 |  |  |
Secured Debt | Ameren Illinois | 4.50% First Mortgage bonds due 2049 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 4.50% |  |  |  |  |  |  |
Debt instrument face amount | $ 500 |  |  |  | 500 |  |  |
Secured Debt | Ameren Illinois | 3.25% First Mortgage bonds due 2050 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 3.25% |  |  |  |  |  |  |
Debt instrument face amount | $ 300 |  |  |  | 300 |  |  |
Secured Debt | Ameren Illinois | 2.90% First Mortgage bonds due 2051 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.90% |  |  |  |  |  |  |
Debt instrument face amount | $ 350 |  |  |  | 350 |  |  |
Secured Debt | Ameren Illinois | 5.90% First mortgage bonds due 2052 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 5.90% |  |  |  |  | 5.90% |  |
Debt instrument face amount | $ 350 |  |  |  | 350 | $ 350 |  |
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Missouri | 2.90% 1998 Series A due 2033 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt interest rate | 2.90% |  |  |  |  |  |  |
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% |  |  |  |  |  |  |
Debt instrument face amount | $ 50 |  |  |  | $ 50 |  |  |

X
- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481139/470-20-50-4 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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