Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Feb. 28, 2021
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 1,780	$ 1,608
Current regulatory assets	(354)	(319)
Regulatory Assets, Noncurrent	1,426	1,289
Regulatory Liabilities	5,445	5,961
Current regulatory liabilities	(136)	(113)
Regulatory Liability, Noncurrent	5,309	5,848
Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	848	650
Current regulatory assets	(254)	(127)
Regulatory Assets, Noncurrent	594	523
Regulatory Liabilities	2,941	3,411
Current regulatory liabilities	(70)	(57)
Regulatory Liability, Noncurrent	$ 2,871	3,354
PISA Deferral Percentage	85.00%
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 908	932
Current regulatory assets	(87)	(180)
Regulatory Assets, Noncurrent	821	752
Regulatory Liabilities	2,377	2,428
Current regulatory liabilities	(64)	(54)
Regulatory Liability, Noncurrent	2,313	2,374
Under-recovered FAC
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	140	47
Under-recovered FAC | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	140	47
Under-recovered FAC | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Under-recovered Illinois electric power costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	33	3
Under-recovered Illinois electric power costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Under-recovered Illinois electric power costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	33	3
Under-recovered PGA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	23	163
Under-recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	23	49	$ 53
Under-recovered PGA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0	114	$ 221
Regulatory Asset, Amortization Period	18 months
MTM derivative losses
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 136	202
MTM derivative losses | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	68	77
MTM derivative losses | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	68	125
IEIMA revenue requirement reconciliation adjustment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	134	42
IEIMA revenue requirement reconciliation adjustment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 134	42
Amortization Period	2 years
FERC revenue requirement reconciliation adjustment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 33	43
Amortization Period	2 years
FERC revenue requirement reconciliation adjustment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0	0
FERC revenue requirement reconciliation adjustment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	11	18
Under-recovered VBA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	17
Under-recovered VBA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Under-recovered VBA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	17
Income taxes
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	185	185
Regulatory Liabilities	$ 1,931	2,066
Weighted-Average Amortization Period	38 years
Income taxes | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 111	115
Regulatory Liabilities	$ 1,095	1,208
Weighted-Average Amortization Period	31 years
Income taxes | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 72	69
Regulatory Liabilities	$ 749	770
Weighted-Average Amortization Period	44 years
Callaway refueling and maintenance outage costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 33	14
Callaway refueling and maintenance outage costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 33	14
Regulatory Asset, Amortization Period	18 months
Callaway refueling and maintenance outage costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0	0
Unamortized loss on reacquired debt
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	54	63
Unamortized loss on reacquired debt | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	47	50
Unamortized loss on reacquired debt | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	7	13
Environmental cost riders
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	64	70
Environmental cost riders | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Environmental cost riders | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	64	70
Storm costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	14	17
Storm costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Storm costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	14	17
Allowance for funds used during construction for pollution control equipment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	11	13
Allowance for funds used during construction for pollution control equipment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	11	13
Allowance for funds used during construction for pollution control equipment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Customer generation rebate program
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	50	47
Customer generation rebate program | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
Customer generation rebate program | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	50	47
PISA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	320	244
PISA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 320	244
Amortization Period	20 years
Regulatory Asset, Amortization Period	20 years
PISA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0	0
Certain Meramec Energy Center costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	51	0
Certain Meramec Energy Center costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 51	0
Regulatory Asset, Amortization Period	5 years
Certain Meramec Energy Center costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0	0
FEJA energy-efficiency rider
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	416	350
FEJA energy-efficiency rider | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0	0
FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	416	350
Other regulatory assets
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	83	88
Other regulatory assets | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	44	41
Other regulatory assets | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	39	47
Over-recovered FAC
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	4	19
Over-recovered FAC | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 4	19
Accumulation Period	4 months
Amortization Period	8 months
Over-recovered FAC | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 0	0
Over-recovered Illinois electric power costs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	13
Over-recovered Illinois electric power costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Over-recovered Illinois electric power costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 0	13
Amortization Period	1 year
Over-recovered PGA
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 10	1
Over-recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Over-recovered PGA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	10	1
MTM derivative gains
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	91	91
MTM derivative gains | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	51	50
MTM derivative gains | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	40	41
Cost of removal
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	2,091	1,988
Cost of removal | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	1,064	1,028
Cost of removal | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	989	929
AROs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	365	603
AROs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	365	603
AROs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Bad debt rider
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	21	19
Bad debt rider | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Bad debt rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	21	19
Pension and postretirement benefit costs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	404	791
Pension and postretirement benefit costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	242	399
Pension and postretirement benefit costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	162	392
Pension and postretirement benefit costs tracker
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	60	28
Pension and postretirement benefit costs tracker | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 60	28
Regulatory Liability, Amortization Period	4 years
Pension and postretirement benefit costs tracker | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 0	0
Renewable energy credits and zero emission credits
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	373	246
Renewable energy credits and zero emission credits | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Renewable energy credits and zero emission credits | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	373	246
RESRAM
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	2	19
RESRAM | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	2	19
RESRAM | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Excess income taxes collected in 2018
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	7	25
Excess income taxes collected in 2018 | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	7	25
Excess income taxes collected in 2018 | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0	0
Other regulatory liabilities
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	86	52
Other regulatory liabilities | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	51	32
Other regulatory liabilities | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 33	17
FAC adjustments | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Accumulation Period	4 months
Asset Retirement Obligation - Nuclear decommissioning trust fund balance | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 958	1,159
Asset Retirement Obligation - removal costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 593	$ 556
Minimum | Under-recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	12 months
Minimum | FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	4 years
Maximum | Under-recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	36 months
Maximum | FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	12 years