Amount of megawatts

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

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Estimated Capital Project Costs

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

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Rate And Regulatory Matters [Line Items]

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

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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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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Percentage of public utility's requested return on equity.

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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) (Detail) $ in Millions	3 Months Ended
	Jun. 30, 2019 USD ($) MWh	Mar. 31, 2019 USD ($)	Dec. 31, 2018 MWh	Jun. 30, 2018 MWh	Mar. 31, 2018 USD ($)
Rate And Regulatory Matters [Line Items]
Total operating revenues		$ 1,556			$ 1,585
Union Electric Company
Rate And Regulatory Matters [Line Items]
Depreciation Percentage Not Included in PISA Deferral		15.00%
Wind Generation Facility \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Amount of Megawatts \| MWh			157	400
Estimated Capital Project Costs		$ 1,400
Final Rate Order \| Natural Gas \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount		2
Pending Rate Case [Member] \| Natural Gas \| Union Electric Company
Rate And Regulatory Matters [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
Public Utilities, Requested Rate Increase (Decrease) on Interim Rates, Amount		6
MEEIA 2013 & 2016 [Domain] \| Final Rate Order \| Electricity \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Total operating revenues		$ 20
MEEIA 2016 \| Final Rate Order \| Electricity \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Total operating revenues					$ 5
Subsequent Event \| Wind Generation Facility \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Amount of Megawatts \| MWh	300
Subsequent Event \| Pending Rate Case [Member] \| Natural Gas \| Union Electric Company
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 1
Public Utilities, Requested Return on Equity, Percentage	9.50%
Public Utilities, Requested Equity Capital Structure, Percentage	50.00%