Summary Of Significant Accounting Policies (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	$ 644	$ 650
Liabilities settled	(7)	(13)
Accretion in period	27	26
Change in estimates	(14)	(19)
Balance	650	644	$ 650
Other current liabilities	282	326
Asset Retirement Obligation Balance [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	23	6
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	640	644
Liabilities settled	(7)	(12)
Accretion in period	27	26
Change in estimates	(14)	(18)
Balance	646	640	644
Other current liabilities	123	103
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	4	6
Liabilities settled	0	(1)
Accretion in period	0	0
Change in estimates	0	(1)
Balance	4	4	6
Other current liabilities	130	177
Asset Retirement Obligation \| Union Electric Company
Asset Retirement Obligation [Line Items]
Noncash Depreciation related to ARO	$ 14	$ 26	$ 31

[Line Items] for Asset Retirement Obligation [Table]

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer.

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Amount of increase (decrease) of physical assets used in the normal conduct of business and not intended for resale, from reclassification, impairment, donation, or changes classified as other. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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