Supplemental Information (Allowance For Funds Used During Construction) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Funds Used During Construction, Rate [Line Items]
Allowance for equity funds used during construction	$ 43	$ 32	$ 28
Allowance for borrowed funds used during construction	17	16	20
Total allowance for funds used during construction	$ 60	$ 48	$ 48
Union Electric Company
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	6.00%	5.00%	6.00%
Allowance for equity funds used during construction	$ 26	$ 19	$ 19
Allowance for borrowed funds used during construction	10	10	12
Total allowance for funds used during construction	$ 36	$ 29	$ 31
Ameren Illinois Company
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	5.00%	5.00%	5.00%
Allowance for equity funds used during construction	$ 17	$ 13	$ 9
Allowance for borrowed funds used during construction	7	6	8
Total allowance for funds used during construction	$ 24	$ 19	$ 17

[Line Items] for Allowance for Funds Used During Construction, Rate

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- Definition

Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Amount capitalized of allowance for funds used during construction.

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- Definition

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

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