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
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]
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 | 3.70% First Mortgage bonds due 2047 | Related Party
Debt Instrument [Line Items]
Long-term debt interest rate	3.70%
Debt instrument face amount	$ (1)							0
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 | 3.25% First Mortgage bonds due 2050 | Related Party
Debt Instrument [Line Items]
Long-term debt interest rate	3.25%
Debt instrument face amount	$ (2)							0
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%
Debt instrument face amount	$ (350)							(350)
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]
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)