Achieved Percentage of Energy Efficiency Earnings For Incentive Award

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Amount of megawatts

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Ameren Missouri's average annual electric efficiency investments under the MEEIA

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The percentage of depreciation not allowed to be deferred under the PISA election.

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- Definition

Estimated Capital Project Costs

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- Definition

Incentive Award if Energy Efficiency Goals Are Achieved

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- Definition

Incentive adder to FERC allowed base return on common equity

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- Definition

Ameren Missouri's electric energy efficiency investments under the MEEIA.

+ References

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- Definition

Deferral percentage of the depreciation expense on certain property, plant, and equipment placed in-service and not included in base rates.

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No definition available.

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- Definition

Percentage of energy customers receive from renewable resources

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- Definition

Value established for a utility on which the entity is allowed to earn a particular rate of return

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No definition available.

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- Definition

Recovery period for plant in service accounting deferrals

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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved rate increase (decrease) by regulatory agency.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Percentage of public utility's requested equity to capital, including debt and equity.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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- Definition

Percentage of public utility's requested return on equity.

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No definition available.

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Rate and Regulatory Matters (Narrative-Missouri) (Details) $ in Millions	3 Months Ended									12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) MWh	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) MWh	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) MWh	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent		$ 4,637				$ 4,387				$ 4,637	$ 4,387
Revenues		1,419	$ 1,724	$ 1,563	$ 1,585	1,399	$ 1,723	$ 1,537	$ 1,515	6,291	6,174	$ 6,076
Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent		2,799				2,664				$ 2,799	$ 2,664
PISA Deferral Percentage										85.00%
Recovery period for plant in service accounting deferrals										20 years
Depreciation Percentage Not Included in PISA Deferral										15.00%
Revenues		713	$ 1,129	$ 955	792	$ 696	$ 1,116	$ 934	$ 791
Union Electric Company \| Electricity
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount										$ 167
Ameren Transmission Company of Illinois
Public Utilities, General Disclosures [Line Items]
Estimated Capital Project Costs										$ 81
Ameren Transmission Company of Illinois \| Mark Twain Project
Public Utilities, General Disclosures [Line Items]
Incentive adder to FERC allowed base return on common equity										0.50%
TCJA - Excess Accumulated Deferred Income Tax Amortization \| Union Electric Company \| Electricity
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount										$ 74
TCJA - Excess Amounts Collected in Rates
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent		60								60
Final Rate Order \| Union Electric Company \| Natural gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		2
Final Rate Order \| Union Electric Company \| MEEIA 2013 \| Electricity
Public Utilities, General Disclosures [Line Items]
Incentive Award if Energy Efficiency Goals Are Achieved										28
Final Rate Order \| Union Electric Company \| MEEIA 2016 \| Electricity
Public Utilities, General Disclosures [Line Items]
Incentive Award if Energy Efficiency Goals Are Achieved										$ 27
Revenues		$ 6			$ 5
Achieved Percentage of Energy Efficiency Earnings For Incentive Award		100.00%								100.00%
Final Rate Order \| Union Electric Company \| MEEIA 2019 \| Electricity
Public Utilities, General Disclosures [Line Items]
Incentive Award if Energy Efficiency Goals Are Achieved		$ 30
MEEIAEnergyEfficiencyInvestments		226
AnnualMEEIAEnergyEfficiencyInvestments		$ 65
Achieved Percentage of Energy Efficiency Earnings For Incentive Award		100.00%								100.00%
Final Rate Order \| Ameren Transmission Company of Illinois \| Mark Twain Project
Public Utilities, General Disclosures [Line Items]
Incentive adder to FERC allowed base return on common equity										0.50%
Pending Rate Case \| Union Electric Company \| Natural gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 4
Public Utilities, Requested Return on Equity, Percentage		10.30%
Public Utilities, Requested Equity Capital Structure, Percentage		51.84%
Rate Base		$ 259
Wind Generation Facility \| Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amount of Megawatts \| MWh		157		400
Estimated Capital Project Costs										$ 1,000
Renewable Choice Program \| Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amount of Megawatts \| MWh										400
Renewable Choice Program \| Union Electric Company \| Electricity
Public Utilities, General Disclosures [Line Items]
Percentage of Energy Received From Renewable Resources										100.00%
Renewable Choice Program - Megawatts Owned \| Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amount of Megawatts \| MWh										200
Maximum
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage										2.85%
Subsequent Event [Member] \| Union Electric Company \| MEEIA 2013 \| Electricity
Public Utilities, General Disclosures [Line Items]
Revenues	$ 9
Subsequent Event [Member] \| Final Rate Order \| Union Electric Company \| MEEIA 2016 \| Electricity
Public Utilities, General Disclosures [Line Items]
Revenues	$ 11