Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
2022	$ 505,000,000
2023	340,000,000
2024	850,000,000
2025	300,000,000
2026	350,000,000
Thereafter	10,837,000,000
Total	13,182,000,000
Ameren (parent)
Debt Instrument [Line Items]
2022	0
2023	0
2024	450,000,000
2025	0
2026	350,000,000
Thereafter	1,750,000,000
Total	2,550,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	17,000,000
Union Electric Company
Debt Instrument [Line Items]
2022	55,000,000
2023	240,000,000
2024	350,000,000
2025	0
2026	0
Thereafter	5,024,000,000
Total	5,669,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	50,000,000
Ameren Illinois Company
Debt Instrument [Line Items]
2022	400,000,000
2023	100,000,000
2024	0
2025	300,000,000
2026	0
Thereafter	3,638,000,000
Total	4,438,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	46,000,000
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
2022	50,000,000
2023	0
2024	50,000,000
2025	0
2026	0
Thereafter	425,000,000
Total	525,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	2,000,000
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	$ 0
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]
2022	50,000,000
Debt instrument face amount	450,000,000.0	$ 450,000,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
2022	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
2024	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Four
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Five
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Six
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Seven
Debt Instrument [Line Items]
Thereafter	76,500,000
Unsecured Debt \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Debt Instrument, Redemption, Period Eight
Debt Instrument [Line Items]
Thereafter	$ 76,500,000

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