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Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($) | Dec. 31, 2022 | Sep. 30, 2022 | Dec. 31, 2021
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Less: Maturities due within one year | $ (340,000,000) |  | $ (505,000,000)
Long-term Debt, Net | 13,685,000,000 |  | 12,562,000,000
Thereafter | 11,358,000,000 |  |
Ameren (parent) |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 2,550,000,000 |  | 2,550,000,000
Less: Unamortized discount and premium | (2,000,000) |  | (2,000,000)
Debt Issuance Costs, Net | (12,000,000) |  | (15,000,000)
Long-term Debt, Net | 2,536,000,000 |  | 2,533,000,000
Thereafter | 1,250,000,000 |  |
Union Electric Company |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 6,139,000,000 |  | 5,669,000,000
Less: Unamortized discount and premium | (12,000,000) |  | (12,000,000)
Debt Issuance Costs, Net | (41,000,000) |  | (38,000,000)
Less: Maturities due within one year | (240,000,000) |  | (55,000,000)
Long-term Debt, Net | 5,846,000,000 |  | 5,564,000,000
Debt Securities, Held-to-maturity | 240,000,000 |  | 248,000,000
Thereafter | 5,149,000,000 |  |
Union Electric Company | City Of Bowling Green Agreement - Peno Creek Ct |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | 0 |  | 8,000,000
Union Electric Company | Audrain County Agreement - Audrain County Ct |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | 240,000,000 |  | 240,000,000
Ameren Illinois Company |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 4,888,000,000 |  | 4,438,000,000
Less: Unamortized discount and premium | (9,000,000) |  | (7,000,000)
Debt Issuance Costs, Net | (44,000,000) |  | (39,000,000)
Less: Maturities due within one year | (100,000,000) |  | (400,000,000)
Long-term Debt, Net | 4,735,000,000 |  | 3,992,000,000
Thereafter | 4,488,000,000 |  |
Ameren Transmission Company of Illinois |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 570,000,000 |  | 525,000,000
Debt Issuance Costs, Net | (2,000,000) |  | (2,000,000)
Less: Maturities due within one year | 0 |  | (50,000,000)
Long-term Debt, Net | 568,000,000 |  | 473,000,000
Thereafter | 471,000,000 |  |
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes 2.50% Due 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 450,000,000 |  | 450,000,000
Long-term debt interest rate | 2.50% |  |
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes365 due 2026 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 350,000,000 |  | 350,000,000
Long-term debt interest rate | 3.65% |  |
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes 1.95% due 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 500,000,000 |  | 500,000,000
Long-term debt interest rate | 1.95% |  |
Unsecured Debt | Ameren (parent) | Senior Secured Notes 1.75% Due 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 450,000,000 |  | 450,000,000
Long-term debt interest rate | 1.75% |  |
Unsecured Debt | Ameren (parent) | Senior Secured Notes 3.50% Due 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 800,000,000 |  | 800,000,000
Long-term debt interest rate | 3.50% |  |
Unsecured Debt | Union Electric Company | 1992 Series due 2022 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 1.60% |  |
Unsecured Debt | Union Electric Company | Senior Secured Notes 2.15% Due 2032 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 2.15% |  |
Unsecured Debt | Union Electric Company | First Mortgage Bonds, 0.375%, $100 Million Due 2023 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 0.375% |  |
Unsecured Debt | Union Electric Company | First Mortgage Bonds, 2.90%, $350 Million Due 2051 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 2.90% |  |
Unsecured Debt | Union Electric Company | First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 3.90% |  |
Unsecured Debt | Ameren Illinois Company | First Mortgage Bonds, 5.90%, $350 Million Due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 5.90% |  |
Unsecured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.85%, Due 2032 - $500 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 0.0385% |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 75,000,000 |  | $ 75,000,000
Long-term debt interest rate | 2.45% |  | 2.45%
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036 | Debt Instrument, Redemption, Period One |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 30,000,000 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036 | Debt Instrument, Redemption, Period Two |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 45,000,000 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | 400,000,000 |  | $ 450,000,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.96%, Due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 95,000,000 |  | 0
Long-term debt interest rate | 2.96% |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.96%, Due 2052 | Debt Instrument, Redemption, Period One |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 45,000,000 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.96%, Due 2052 | Debt Instrument, Redemption, Period Two |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 50,000,000 |  |
Secured Debt | Union Electric Company | Senior Secured Notes350 Due2024 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 350,000,000 |  | 350,000,000
Long-term debt interest rate | 3.50% |  |
Secured Debt | Union Electric Company | Senior Secured Notes, 2.95%, Due 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 400,000,000 |  | 400,000,000
Long-term debt interest rate | 2.95% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 3.50%, Due 2029 - $450 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 450,000,000 |  | 450,000,000
Long-term debt interest rate | 3.50% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 465,000,000 |  | 465,000,000
Long-term debt interest rate | 2.95% |  |
Secured Debt | Union Electric Company | Senior Secured Notes 2.15% Due 2032 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 525,000,000 |  | 525,000,000
Long-term debt interest rate | 2.15% |  |
Secured Debt | Union Electric Company | 5.50% Senior secured notes due 2034 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 184,000,000 |  | 184,000,000
Long-term debt interest rate | 5.50% |  |
Secured Debt | Union Electric Company | 5.30% Senior secured notes due 2037 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 300,000,000 |  | 300,000,000
Long-term debt interest rate | 5.30% |  |
Secured Debt | Union Electric Company | 8.45% Senior secured notes due 2039 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 350,000,000 |  | 350,000,000
Long-term debt interest rate | 8.45% |  |
Secured Debt | Union Electric Company | 3.90% Senior secured notes due 2042 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 485,000,000 |  | 485,000,000
Long-term debt interest rate | 3.90% |  |
Secured Debt | Union Electric Company | Senior Secured Notes, 3.65%, Due 2045 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 400,000,000 |  | 400,000,000
Long-term debt interest rate | 3.65% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 4.00%, Due 2048 - $425 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 425,000,000 |  | 425,000,000
Long-term debt interest rate | 4.00% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 3.25%, Due 2049 - $330 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 330,000,000 |  | 330,000,000
Long-term debt interest rate | 3.25% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 550,000,000 |  | 550,000,000
Long-term debt interest rate | 2.625% |  |
Secured Debt | Union Electric Company | First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 525,000,000 |  | 0
Long-term debt interest rate | 3.90% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 2.70%, Due 2022 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 0 | $ 400,000,000 | 400,000,000
Long-term debt interest rate | 0.027% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 0.375%, $100 Million Due 2023 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 100,000,000 |  | 100,000,000
Long-term debt interest rate | 0.375% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 3.25%, Due 2025 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 300,000,000 |  | 300,000,000
Long-term debt interest rate | 3.25% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.125% Due 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 60,000,000 |  | 60,000,000
Long-term debt interest rate | 6.125% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.80%, Due 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 430,000,000 |  | 430,000,000
Long-term debt interest rate | 3.80% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 1.55%, Due 2030 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 375,000,000 |  | 375,000,000
Long-term debt interest rate | 1.55% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 61,000,000 |  | 61,000,000
Long-term debt interest rate | 6.70% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 42,000,000 |  | 42,000,000
Long-term debt interest rate | 6.70% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes 4.80% Due 2043 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 280,000,000 |  | 280,000,000
Long-term debt interest rate | 4.80% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes 4.30% Due 2044 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 250,000,000 |  | 250,000,000
Long-term debt interest rate | 4.30% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 4.15%, Due 2046 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 490,000,000 |  | 490,000,000
Long-term debt interest rate | 4.15% |  |
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 3.70%, Due 2047 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 500,000,000 |  | 500,000,000
Long-term debt interest rate | 3.70% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 4.50%, Due 2049 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 500,000,000 |  | 500,000,000
Long-term debt interest rate | 4.50% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.25%, Due 2050 - $300 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 300,000,000 |  | 300,000,000
Long-term debt interest rate | 3.25% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 2.90%, $350 Million Due 2051 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 350,000,000 |  | 350,000,000
Long-term debt interest rate | 2.90% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 5.90%, $350 Million Due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 350,000,000 |  | 0
Long-term debt interest rate | 5.90% |  |
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.85%, Due 2032 - $500 Issuance |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 500,000,000 |  | 0
Secured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 3.43% |  |
Secured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.96%, Due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt interest rate | 2.96% |  |
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1992 Series due 2022 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 0 |  | 47,000,000
Long-term debt interest rate | 1.60% |  |
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series A due 2033 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 60,000,000 |  | 60,000,000
Long-term debt interest rate | 2.90% |  |
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series B due 2033 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 50,000,000 |  | 50,000,000
Long-term debt interest rate | 2.90% |  |
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series C due 2033 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 50,000,000 |  | $ 50,000,000
Long-term debt interest rate | 2.75% |  |

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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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