Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) MWh
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	$ 799
Unrecorded Unconditional Purchase Obligation, Due within Two Years	445
Unrecorded Unconditional Purchase Obligation, Due within Three Years	301
Unrecorded Unconditional Purchase Obligation, Due within Four Years	142
Unrecorded Unconditional Purchase Obligation, Due within Five Years	79
Unrecorded Unconditional Purchase Obligation, Due after Five Years	166
Unrecorded Unconditional Purchase Obligation	1,932
Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	349
Unrecorded Unconditional Purchase Obligation, Due within Two Years	160
Unrecorded Unconditional Purchase Obligation, Due within Three Years	121
Unrecorded Unconditional Purchase Obligation, Due within Four Years	72
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	702
Natural gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	197
Unrecorded Unconditional Purchase Obligation, Due within Two Years	143
Unrecorded Unconditional Purchase Obligation, Due within Three Years	77
Unrecorded Unconditional Purchase Obligation, Due within Four Years	27
Unrecorded Unconditional Purchase Obligation, Due within Five Years	7
Unrecorded Unconditional Purchase Obligation, Due after Five Years	34
Unrecorded Unconditional Purchase Obligation	485
Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	25
Unrecorded Unconditional Purchase Obligation, Due within Two Years	43
Unrecorded Unconditional Purchase Obligation, Due within Three Years	59
Unrecorded Unconditional Purchase Obligation, Due within Four Years	14
Unrecorded Unconditional Purchase Obligation, Due within Five Years	42
Unrecorded Unconditional Purchase Obligation, Due after Five Years	31
Unrecorded Unconditional Purchase Obligation	214
Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	157
Unrecorded Unconditional Purchase Obligation, Due within Two Years	54
Unrecorded Unconditional Purchase Obligation, Due within Three Years	10
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	221
Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	4
Unrecorded Unconditional Purchase Obligation, Due within Three Years	4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	29
Unrecorded Unconditional Purchase Obligation	47
Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	67
Unrecorded Unconditional Purchase Obligation, Due within Two Years	41
Unrecorded Unconditional Purchase Obligation, Due within Three Years	30
Unrecorded Unconditional Purchase Obligation, Due within Four Years	26
Unrecorded Unconditional Purchase Obligation, Due within Five Years	27
Unrecorded Unconditional Purchase Obligation, Due after Five Years	72
Unrecorded Unconditional Purchase Obligation	263
Union Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	467
Unrecorded Unconditional Purchase Obligation, Due within Two Years	264
Unrecorded Unconditional Purchase Obligation, Due within Three Years	225
Unrecorded Unconditional Purchase Obligation, Due within Four Years	120
Unrecorded Unconditional Purchase Obligation, Due within Five Years	75
Unrecorded Unconditional Purchase Obligation, Due after Five Years	130
Unrecorded Unconditional Purchase Obligation	1,281
Union Electric Company | Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	349
Unrecorded Unconditional Purchase Obligation, Due within Two Years	160
Unrecorded Unconditional Purchase Obligation, Due within Three Years	121
Unrecorded Unconditional Purchase Obligation, Due within Four Years	72
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	702
Union Electric Company | Natural gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	40
Unrecorded Unconditional Purchase Obligation, Due within Two Years	31
Unrecorded Unconditional Purchase Obligation, Due within Three Years	15
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	14
Unrecorded Unconditional Purchase Obligation	108
Union Electric Company | Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	25
Unrecorded Unconditional Purchase Obligation, Due within Two Years	43
Unrecorded Unconditional Purchase Obligation, Due within Three Years	59
Unrecorded Unconditional Purchase Obligation, Due within Four Years	14
Unrecorded Unconditional Purchase Obligation, Due within Five Years	42
Unrecorded Unconditional Purchase Obligation, Due after Five Years	31
Unrecorded Unconditional Purchase Obligation	214
Union Electric Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	0
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	$ 0
Amount of Megawatts | MWh	102
Union Electric Company | Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	$ 4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	4
Unrecorded Unconditional Purchase Obligation, Due within Three Years	4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	29
Unrecorded Unconditional Purchase Obligation	47
Union Electric Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	49
Unrecorded Unconditional Purchase Obligation, Due within Two Years	26
Unrecorded Unconditional Purchase Obligation, Due within Three Years	26
Unrecorded Unconditional Purchase Obligation, Due within Four Years	26
Unrecorded Unconditional Purchase Obligation, Due within Five Years	27
Unrecorded Unconditional Purchase Obligation, Due after Five Years	56
Unrecorded Unconditional Purchase Obligation	210
Ameren Illinois Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	322
Unrecorded Unconditional Purchase Obligation, Due within Two Years	171
Unrecorded Unconditional Purchase Obligation, Due within Three Years	72
Unrecorded Unconditional Purchase Obligation, Due within Four Years	22
Unrecorded Unconditional Purchase Obligation, Due within Five Years	4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	20
Unrecorded Unconditional Purchase Obligation	611
Ameren Illinois Company | Natural gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	157
Unrecorded Unconditional Purchase Obligation, Due within Two Years	112
Unrecorded Unconditional Purchase Obligation, Due within Three Years	62
Unrecorded Unconditional Purchase Obligation, Due within Four Years	22
Unrecorded Unconditional Purchase Obligation, Due within Five Years	4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	20
Unrecorded Unconditional Purchase Obligation	377
Ameren Illinois Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	157
Unrecorded Unconditional Purchase Obligation, Due within Two Years	54
Unrecorded Unconditional Purchase Obligation, Due within Three Years	10
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	221
Ameren Illinois Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	5
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	13
Ameren Illinois Company | Zero Emission Credits
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Unrecorded Unconditional Purchase Obligation	$ 26