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
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